Ironic.... I was just having a discussion with someone the other day about arguing politics and religion. Someone said "name one accomplishment Obama had done in his presidency that wasn't horrific." So the person started naming some things. With each thing offered, the other guy refused to accept it. So at the end of an hour one guy was still convinced Obama hadn't done one good thing and the other guy was convinced his buddy was closed minded and refuses to admit he's wrong. Kind of reminded me of an atheist and a christian arguing over contradictions or prophecies in the bible. It's pointless.
All a believer can do when speaking to an atheist is try and understand their perspective, give insights into objections they have, answer questions where able and simply demonstrate that they represent Christ.
The discussion can feel pointless to some, but I don't speak about my faith hoping to convert an atheist to Christ. Now, if that happens then awesome, but I'm under no delusion that it will....firm choices have been made.
I'm speaking to those that haven't made a choice and that aren't speaking because they may not know what to say. Atheists and agnostics are at the forefront of most discussion because they have made a definite choice about God and choose to voice it and engage theists. I use those dialogues as opportunities to provide the other side of the coin - the Christian answer to the atheist question. I'm not always successful, but I learn as I go.