If you create a situation where everybody is constantly armed with (presumably) loaded weaponry and has the skill to use it, then yes - it will most likely reduce some forms of impulsive crime, like spur of the moment-type muggings on the street. However, it creates a whole new bag of problems:
1) Domestic violence can quickly evolve into domestic murder when guns are freely available, and anyone can reliably use them. Plus, it's much easier for firearm accidents to happen when you are involved with them constantly.
2) Even if you'll deter some impulsive crime, you won't stop determined/desperate criminals just because more people have guns - instead of holding you up, the crooks will just end up shooting first with bigger guns. Which can also create an arms race between the legislature, the police and crime.
3) Combine the previous point with the fact that anyone and everyone you meet has the power to kill you within seconds, anytime - and you'll get a nice little feeling of society-wide paranoia. Works wonders for your mental health.
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