My reasons not to buy firearms:
1) They're expensive, especially when you take the safety precautions and training into consideration;
2) Nearly everyone I know has been troubled with suicidal ideation, and we've discussed that we don't want firearms around because we're afraid of the temptation;
3) I don't think they're effective for individual self-defense, only for coordinated groups, so basically you'd want a militia and an armory, not individual ownership.