Are people really calling up doctors and asking them to perform surgery on them for free?
Probably not, but if your friend is a doctor and you call him up asking what's the best thing to do for the flu, he'll gladly tell you get lots of rest and drink plenty of fluids.
Are they calling up mechanics and asking them to swap out an in-tank fuel pump for them?
Half the lights were out in my car, and mechanic friends chewed my ass upwards and downwards for paying a mechanic. "Dude, that's maybe thirty bucks worth of parts! I'd have fixed it for you!"
I'll troubleshoot a friend's PC problem unless it's going to involve a shitload of work, like changing an in-tank fuel pump would.
The problem I have is people just assuming that I will take a couple of hours out of my day to do something for them, but then being unwilling to either reciprocate the favor, or offer me something like a beer for it.
Maybe you're hanging out with the wrong crowd? I know there are a lot of people I associate with that I'd be better off avoiding.
The goal of science is to build better mousetraps. The goal of nature is to build better mice.