Originally posted by orfeo
Despite the tone of sarcasm that was apparently said in, it's worth considering the question further. Who is more likely to actually shape the world they live in - someone who is just 'getting on with living', or someone who strongly believes in certain things?
I've enjoyed all of the responses so far. Very sincere.
Before I respond directly to your question, let me clarify that I'm reading into your post here a bit by assuming you mean "shape the world they live in" to be a positive action. It should be obvious immediately upon a moments reflection that such an action need not be positive at all!
Another problem with the question is that it equates non-theists with people who do not strongly believe in any certain things. This, however, is not a true relation. Atheists may have strong beliefs in many causes. The only thing that necessarily seperates theists from non-theists (i.e. atheists) is the belief in at least one god. Two people, one theist and one atheist, can share a great number of other beliefs (e.g. the importance of preserving the planet, our duty to educate our children and care for our families, the benefit of helping the poor and sick). These shared beliefs may cause both people to influence the world in a positive way. Note that it is true that theists and non-theists may share other beliefs that lead them to influence the world negatively as well.
Now from a structural point of view*, it is not obvious to me that the theist should be more concerned with shaping the world in a positive manner, especially if such an enterprise is costly (in terms of finances, effort, or perhaps status). Consider that all theists can be divided into two groups: those that believe in an eternal afterlife and those that do not. For those that do believe in an eternal afterlife, the optimal amount of positive "world-shaping" is that level which is just enough to reward them with the good afterlife payoff (heaven). Any additional effort is suboptimal since any improvement comprises only an infintesimal fraction of their entire life (earthly life + afterlife). Think of a game where you must build a sand castle to get $1,000,000. Time spent building the sand castle comes at the cost of effort and lost income from an outside source. Moreover, at some point the tide will come in and wipe the sand castle away. In such a game, the optimal strategy is to build the bare minimum of what satisfies "a sandcastle" and collect the $1,000,000. Any additional effort comes at the costs described above with no change in payoff, and of course, it will all be destroyed anyway.
Now for theists who do not believe in an infinite afterlife, the incentive to shape the world positively grows because the improvement comprises a larger fraction of their whole life. The increased proportion of their earthly life to their whole life causes them to place more weight on earthly matters.
So for atheists, most of whom do not believe in an afterlife**, the entire weight is placed on earthly matters. Life on earth is precious precisely because it is temporary. Therefore the atheist should work at least as hard, if not harder, to shape the world that they live in.
Ironically, I've heard evangelicals use this same argument, but as a perjorative. Perhaps you've heard the following as well: "If there's no afterlife, and here and now is all there is, then atheists should be raping and stealing all the time, because who cares what happens?"
Certainly if one is predisposed toward raping and stealing, the absence of some long or even infinite punishment will come as a comfort; however, there is no reason to think that atheists are any more predisposed toward raping and stealing than anyone else. The majority wish to make the world a better place. Given the view that this life is all that there is, the atheist actually has at least as strong or stronger incentive to work toward that noble goal than does his theist counterpart.
* - by structural, I mean that I will examine the incentives created by the system itself. It does not mean that all theists of a certain type will always behave one way and all atheists will behave another way.
** - being an atheist does not necessarily imply that you do not believe in an afterlife, however, most do not.