The power of the Second Amendment
Any limit would amount to a violation of the Second Amendment.
Bad guys can always have access to guns even if it’s illegal. So you have to allow good guys to buy guns to defend themselves.
Enter the background of the argument here ...
When someone is intent on committing a terrible crime with a gun, they will source it by any means necessary - whether they are illegal is immaterial. The only way to stop these crimes is if regular, law-abiding citizens are also able to own guns and can therefore protect themselves and others from terrible crimes.
The world does not exist in the binary of 'good guys' and 'bad guys'. Even if ensuring everyone had guns did mean 'good guys' could stop 'bad guys' from committing crimes, this does not address all the gun deaths and injuries that are not the result of criminal intent, such as suicide and accidents. The fantasy that this would work, also, is a complete fallacy. Any number of things can go wrong with using a gun to deter a shooter, even if the intent is good. A bystander may be shot, or a criminal may just steal a 'good guy's' gun. The more people overall that own a gun, the higher the homicide rate. Those who do own a gun are more likely to be killed or injured than those who don't.
Enter the framing of the argument here ...
[P1] Bad guys have access to guns and are going to commit crimes with them. [P2] The only realistic way to stop this is to ensure good guys also have guns in order to protect themselves.
[Rejecting P1] If 'bad guys' have guns, the government should ensure they take access away from them. [Rejecting P2] Giving 'good guys' guns does not necessarily ensure safety.
Enter more information about the argument here ...