Do some people use Christianity as an excuse to do good for others?

I go to church with my family (I'm an atheist [or agnostic, still researching and deciding]) and see that a lot of people do a lot of nice things around the world, but all of them involve spreading God's word or something like that. I'm not saying their methods are COMPLETELY wrong, but if it's necessary. I'm also wondering if that's the only reason people do it, or even if they would at all had they not been Christian? ((btw, i'm just using christianity as a religious term, since i haven't really experienced catholicism or other religions))