Why shouldn't a psychic charge for their services? They are taking time and energy away from their day to provide a service for someone else. That's time and energy they could be using to make money doing something else.
Why are they the only ones that should be expected to provide their gifts in life for free. You wouldn't expect someone who sings professional to do it for free. You wouldn't expect a doctor to work for free, a house cleaner, a dog walker.
I have a friend who does Reiki. She loves it, loves helping people. Would love nothing more to do it full time, but she's afraid that if she excepts money people won't take her seriously.
She spent a lot of money to learn what she does. The table costs money, the things she uses costs money, the magazines to keep up to date. Why shouldn't she be able to charge without feeling guilty?
All the ones I know are good hard working people trying their best just like everyone else. Most do classes so you can learn to do this stuff on your own. It's not some secret they are keeping from you.
But like anything else, sometimes it's just nice to have someone else do it for you. I can paint my own nails, but sometimes it's nice to go for a manicure. Actually I've never done it, but you get my point.
Of course, like with every profession, you'll have a bad apple here or there who's only in it to milk people. But most of these people are not scam artist.