This part, must mean you associate with the wrong crowd. Probably only met people from the entertainment, massage and bar scene.
So, you feel that you can not trust the ones you call Thai friends, or you have not been giving them all your money as they still have the friendliness left? How is it?
Nah, it´s not really the culture, it´s more like a result of depressing a big part of the population for ages. Yeah, it´s backwards, as they have not been focusing on education for the bigger part of the population.
I assume you have been living in Bangkok, Pattaya, Phuket or another of the very tourist populated places. That´s probably why you are not happy, combined with that you must have been seeking your friends in the wrong places. Where I live, I get smiles from people as soon as I open the door and go out.