My last question got me verbally abused, so let's try this again...?

My last question was "why do atheists spend so much time in the R&S section?" People went nuts saying the Christians are trying to invade this section, blah, blah, blah. So, let me rephrase and get to the point I'm trying to make. Why do atheists spend so much time thinking about religions, or the lack thereof, if they are convinced they already know the "truth?" Christianity tells us to spread the word to others, but do atheists have that same philosophy? Do they feel the need to spread the lack of religion? Again, I'm certainly not trying to bash anyone, just genuinely curious if they've ever asked themselves why they think about this so much?