They ARE a reasonable defense against reasonable against criminals in an ideal world. However, the practical, power-mongering, and "military society" issues are far too large for anyone to implement successfully. So, the answer is yes - but this doesn't mean it's a good idea in and through reality systems, everyone.
Obviously it's reasonable defense, that much is easily agreed upon. In the ideal situation, women is cornered in alleyway by man, man gropes women, women pulls out pistol and pops him one in the knee. The reality of it is though, if everyone were carrying around revolvers and knives, there would be no discerning the criminals from the innocents.
Honestly, if people had good judgement and excersized good responsibility, then the arming of citizens for self defense would be A-OK. Now, what percentage of the world do you think would use weapons with safety, responsibility, and general non-stupidity? ...Yeah, the world would become a complete shootout. But "Oh, we can just put them through tests to see if they are viable for the possesion of weapons!" Until we have mindreaders, there is no way to know what the person intends to do with his 'self defense weapon'. In the shooting range he seems like a man concerned about his safety. Out there, he's itching to get even with that guy he was bullied by in high-school.
So yes, guns and weapons are equalizers for innocents v.S. Criminals. This much is easy to agree on.
But is it practical to be licensing weapons to people for self defense? I doubt it.
Criminals don't pick victims that they think are likely to resist enough to cause the criminal injury. Repeated studies have shown that criminals are more afraid of an armed victim than they are of police. And guns are the only realistic means a 110lbs woman can use to resist an attack by a 200lbs rapist.
Its just like war just because you oppose violence doesn't mean the other side is going to hesitate to kill you if they wanted to. I think for this reason its perfectly logical weapons for defense. I don't know about anyone else but I have never heard of a criminal all of a sudden having a change of heart when robbing you.
If everyone had a gun is public, than one gunshot and everyone will accidentally shoot each other in the chaos. And at home, you'll likely be caught off guard (although I have a small knife near my bed). In a secluded or fairly empty area, a small weapon would be a great way to intimidate a lone assailant, but avoiding them and drawing attention would be far more effective. Maybe a small non-lethal weapon, but not a large knife or a firearm.
I strongly demands that to better protect ourselves, we must arm and enable yourself with more than just guns or melee weapons! Look around you, humans are sinful in nature, no matter what we do, profit and self gratification must come first! Therefore, a stepping future ahead will always bring crimes at a upper hand! Have you ever wonder, what catches a criminal? Answer: A criminal!
Guns kill people. Thus, it is completely unreasonable to say it is reasonable to use a deadly weapon to prevent theft, fraud and other minor crimes. Furthermore, now anyone can claim self-defense when they kill someone (Zimmerman come to mind?) and kill at will and claim that they were having a crime committed against them.