Does socialism destroy altruism?

I dislike giving homeless people money (I do it anyway), because I feel that that's why we pay for government welfare. If there was no welfare, hence lower taxes, I think I would give more money, however. I've also heard that while Europe's governments give more foreign aid, our personal donations are significantly higher. So does government redistribution of wealth hurt personal charitable contributions? Would people as a whole give more or less if there was no welfare system in place?