Sam Harris writes in The End of Faith:

The philosopher Peter Unger has made a persuasive case that a single dollar spent on anything but the absolute essentials of our survival is a dollar that has some starving child's blood on it.

Well, that caught my attention and I've been thinking about it for a while. The book in question is Living High and Letting Die by Peter Unger, and I had to order it and see what it was all about!
In the meantime, I found out about Utilitarianism, which is the ethical doctrine that basically says you should do whatever maximizes global happiness (or minimizes global suffering). One consequence is that there is no such thing as a victimless crime - another idea I first encountered in Sam Harris's book and I completely agree with it.

Utilitarianism captures very elegantly what I've been thinking for a long time about ethics and such - so I guess I'm a Utilitarian!