Why do Atheists Argue with Christians?

Just a quick question as to why atheists argue with Christians. I don't really understand it. Basically, the atheist has said that there is no god and that we are basically going to die and turn to dust and that is the end of our lives. If that is the case, what does it profit to argue with someone about their beliefs. If you truly believe that we just die and become dust, is it not just wasted breath and time to argue someone's beliefs? The only reasons that I can think is to try and demean Christians (and bring up anything bad that was done while invoking the Christian name) and to make themselves feel better about living in their sin or to try and make themselves feel more intellectual.

Basically, it is saddening that atheists have not come to a knowledge of Jesus who is the only One unto salvation. May God have mercy on all those that do not know Him right now and allow them to come to Him before returning for His bride.