Geez...I'm not an atheist, but I actually have to agree with you. No one's got proof either way. IT IS the flavor of your security blanket! and to quote Jimmy Buffet..."I thought to myself, what the hell's wrong with that?" ;)

So...for a Christian the question must be: Is the drive and ambition in our lives motivated by the recognition you'll receive during your life, or for how you'll be rewarded in the afterlife?~~~

I have to admit, I live as morally as I can muster it for the afterlife. (as a Christian..you would expect that right?).

But as for drive and ambition and recognition...I'd have to admit, I'm living for the here and now... I have a good brain, a healthy work ethic, and a strong drive and desire to be successful. I figure ...I should make the most of it. So in that way, we're not so very different. I like money. I like things. I like the art of living.
but
Sometimes there's some pretty serious conflicts when the two challenge each other. I guess I could say its my faith that makes me think..before doing something that I "morally" might regret. There are times when I was in business that I would have really felt uncomfortable with the strategy I would have had to have taken to achieve the monetary outcome of a deal. The only reason I felt that way, is because of my faith. If I had no faith, and no perceived feeling of repercussion from my God...I don't know? Maybe I would have proceeded. There were no legal issues involved. Just a matter of something I felt personally, was wrong. It crossed my line so to speak. Maybe I'd be really rich right now? ! But at this point I don't have any regrets about those choices.

So...I guess its sort of a "stop-bar" when I think there might be something that could complicate my hopes for the here after. I can see where that might seem silly to some people.

Its like a self imposed regulatory code, isn't it?

That said... I still don't understand why people would try and force this down your (atheist) throats. For all anybody knows...You may be right. Maybe there's nothing at all after this life and I'm reigning myself in for nothing?! On the otherhand...If I'm going to even entertain the idea of a here-after...(speaking only for myself here) I'd rather be safe than sorry.
I'll go out on a limb and say that: I would bet that if these Christians you are talking to were perfectly honest about it...that would be their reason too. Its just a bet. I wouldn't count on getting them to admit it, because it sounds selfish...and they probably would avoid that label.
Bottom line is, my "regulatory code" as it is, is not something for me to put on anybody else. Its personal.

Anyhow...sorry to interrupt your discussion, but I thought you might be interested in a perspective that might not be so fundamentalist. I have to say, it bothers me that they are constantly challenging your personal decision to live your life the way you want to. It seems to perpetuate an intense dislike for one another and its not really necessary or very productive. I honestly believe there is a great deal to be learned from each other.