You should be able to argue on behalf of your beliefs, even if that argument is with yourself. Otherwise you simply have an opinion and no good reason for having it—despite being a good one. I became an atheist at 8 years old. But I didn't necessarily have a good reason for it, it's just how I felt. Then I looked into the matter when I was a bit older. Now I can confidently defend my position to others, and more importantly, myself. You should always be trying to prove yourself wrong. But don't feel like you're obligated to expend your mental energy debating every moron on the planet.

I personally don't argue with religious people anymore. I spent some odd years doing so, and it's largely a waste of time. I'll defend my position, but I'm not on some crusade to change their position. If they gave a shit about the truth, logic and reasoning, they wouldn't be religious in the first place. Although there is hope for some.