The definition of libertarian I was referring to is the American right wing libertarian.
Basically it's a childishly selfish belief that you owe nothing to the society that supports you and everything would be better if people were left alone to neglect and abuse each other.
That's an unfair exaggeration, of course, but not by much. It's basically rebranded anarcho-capitalism and idealised selfishness disguised in rhetoric about liberty and self-determination.
If you're going to be part of society, you should pay your part and if not, you should watch out for bears.
First, your server isn't getting anything for free, they're working for their wage and tips.
Second, when it comes to the absolute basics necessary to survive then yes, people who could not otherwise afford to live should ABSOLUTELY get things for free.
Stiffing your server DOES affect others, though.
True, but right now it's the least bad alternative to starving and homeless servers.
Which is even worse for the servers since fewer customers means fewer tips and may eventually mean getting fired.
You're basically taking food out of the mouths of those who (used to) serve you and their children.