There are a lot of arguments for why tactical rifles, incorrectly labeled "assault weapons" in the media, should be banned. Most of the arguments against "assault weapons" are the same arguments used against firearms of any kind.
Many of these arguments have propagated through the media for decades, and even though judicial courts have addressed some of them, they keep marching on. By continuing to bring up the same trite points, they show that in the battle of reasoning, they are unarmed [pardon the 2nd pun, I couldn't resist]. They are probably also hoping that you haven't read the counter points in this discussion.
1] Anti-gun proponents claim that because the 2nd Amendment contains a clause that includes "a well regulated militia" as it reads
A well regulated militia being necessary to the security of a free state, the right of the people to keep and bear arms shall not be infringed
that households are not entitled to guns. This is an argument made by people who haven't done a shred of research. To be able to form a militia, a necessary condition would be to have ready access to guns. The alternative suggestion that the anti-gun proponents are making is that you would have to go up to your oppressive government and request a license to form a militia so that you can obtain firearms to fight against them. Yeah, I see that one working out well. C'mon, use your head. This right to personal firearms was only slightly unclear for about 5 years after ratification of the Constitution until the individual right (and as it reads, perhaps a requirement) to arm was retained and strengthened by the Second Militia Act of 1792.
Interpretation of the law varied from state to state and city to city and lower courts generally dealt with any cases related to the Second Amendment as they came up. Many cities including Washington D.C. and Chicago passed various ordinances banning handguns and other firearms they didn't like and the laws remained on the books for decades. It was only until recently that higher courts got involved and started making significant rulings.
In regards to an interstate firearms transportation case, in 2001, United States v. Emerson, the United States Court of Appeals for the Fifth Circuit held that the Second Amendment to the United States Constitution guarantees individuals the right to bear arms. Then in 2008, in District of Columbia v. Heller, the Supreme Court of the United States held that the Second Amendment to the United States Constitution protects an individual's right to possess a firearm for traditionally lawful purposes, such as self-defense within the home and within federal enclaves. It struck down the D.C. law and determined that handguns are "arms" for the purposes of the Second Amendment. Cities, such as Chicago, still felt that these ruling did not apply to them because the courts only mentioned states and federal enclaves and not local ordinances. This was ultimately decided by the Supreme Court in 2010, with the landmark ruling in McDonald v. Chicago, which held that the "Second Amendment was incorporated under the Fourteenth Amendment thus protecting those rights from infringement by local governments."
It should be noted that within four days, Chicago implemented a de facto ban on handguns by adopting the Responsible Gun Owners Ordinance, a number of draconian restrictions on owning firearms. These restrictions included requiring owners to have certified classroom and range training, but banning ranges in the city limits, banning gun stores inside city limits, not allowing a gun owner to step into their garage with their firearm, only allowing one working firearm in the home at any given moment, and owners had to visit multiple locations to register the gun yearly along with licensing fees.
Part of this ordinance was overturned with Ezell v. Chicago. The city had argued that applicants could obtain their training at gun ranges outside the city. The court opinion noted that Chicago could not infringe Second Amendment rights on the grounds that they could be exercised elsewhere, any more than it could infringe the right to freedom of speech on the grounds that citizens could speak elsewhere [page 20].
Some of the other ordinances are currently being challenged in court, and may take years to resolve.
2] "The "Second Amendment" was written 220 years ago when 3.9 million people lived in America and the most powerful guns available were single-shot flint-lock muskets."
The First Amendment was written 220 years ago when the word "press" meant having an iron machine the size of a Chevy Suburban with movable type that rolled out copies of paper. It didn't say anything about radio, TV or the internet, so should we assume that freedom of speech doesn't apply to those? The Constitution has been ruled to be a "living document" that applies reasonable standards to modern life. I'd also like to add that those "most powerful guns available" were also the same guns that the military had at the time. The real purpose of "assault" rifles is so the citizens have comparable weapons to the military's.
3] "Guns make it much, much easier for people to kill people."
Well, I would hope so, given that that is the point of what a "gun" is for. I don't know about you, but when I buy a car, I want it to be able to drive. Obviously, it is supposed to be used in a responsible and law abiding manner but there will always be law breakers and people can misuse anything. They can drive a car into crowd, or stab people with knives. Or do both.
4] "Nothing will stop people from going crazy, therefore, we should rid ourselves of these devices that crazy people will get a hold of"
So because .003%* of citizens may misuse a device in a given year, you feel that everyone should have their rights taken away? Shouldn't that then apply to cars since some small percentage misuse them and kill people? How many law abiding citizens have guns out there and are using them responsibly?
5] "Anyone who thinks a few assault weapons will allow citizens to resist tyranny and overthrow our government hasn't seen the weaponry our military has developed in the past 200 years. Your little "militia" is going to hold off the U.S. Army, Navy, Air Force, and Marines? Keep dreaming."
There are 1.4 million active service members in the US military. There are 115 million households in the US. If we assume that at least one adult from each household is an able-bodied person capable of firing a weapon, then there are 82 militia civilians per military servicemen. The Marines may be good, but they aren't that good. Clearly, having decent rifles and munitions to fight this force would be required. Bringing a musket to a machine gun fight wouldn't exactly be a fair fight. Sure, if the Army pulled out the tanks and nuclear weapons they could level the country, but would that kind of a takeover be what they want? No. They would have to fight with infantrymen occupying cities and controlling the people and means of production. After ten years in the War Against Terror, how is it that those little 'ole uneducated, poor, cave dwellers in Afghanistan are still giving the great military might of the USA such a hard time? Because they aren't throwing rocks.
6] "The only thing having MORE guns in schools, malls, theaters, and other public places would do is increase the number of gun-related deaths."
This is debatable. Furthermore, millions of guns are already out there. Passing laws against law abiding citizens certainly isn't the solution since criminals by definition don't obey laws. Schools have been "Gun Free Zones" since 1990, so why didn't that stop Adam Lanza?
7] "Banning assault weapons would not completely eliminate mass shootings, but they might help."
Kind of like how banning cars might help prevent vehicular homicide, right? But let's look at the data shall we? Last year, only 323 people died by a rifle. That's out of 8,583 firearm murders. And an "assault" rifle is a subset of the rifle category. The simple fact of the matter is that "assault" rifles are rarely used to commit murder. More people are killed with blunt objects (496), knives (1,694), and bare hands (728) every year. And if these weapons are banned, will it really have much of an impact on the bottom line? Let's take a look: In 2003, assault rifles had been banned for almost 10 years. How many deaths by rifle that year? 392. These trends hold in nearly the same ratio no matter what year one is looking at.
So the next time someone starts arguing with you about why guns should be outlawed, remind them that it's called the Bill of Rights, not the bill of suggestions.
*8,000 firearm murders / 311 million citizens (Lower bound ratio assuming that there is only one murder per murderer, whereas usually there is more than one murder per murderer).