I hope libertarians are selfish. As Ayn Rand said, rational self-interest is a virtue.
Can you imagine the hell of a world where most people weren't selfish? In that case, having more than another person would be evil. To be good, you'd have to give away all of your stuff until you had less than everyone else--and then they would be the evil ones, and would have to give THEIR stuff away...
The evil Christian ideal of selflessness leads to ever increasing poverty and a downward spiral as each person strives to be better by living their life for someone else. Instead, each person should strive to attain the best they can for themselves. By doing that, you end up helping everyone.