I don't have any experience trading with US brokers, so I can't say if all brokers US-based are scams, but as I know not all brokers accept clients from the US, maybe about regulated, now I use FXOpen, and also this company doesn't accept the client from the US.
I don't think you have to be such categorical regardless US brokers. Not all of them are scammers. Of course, without of any doubt there are some brokers who are rel scammers, you make a deposit then either you lose anything (for some weird reasons) or you won't be able to do a withdrawal. I guess that everybody has to learn its broker by details, look through licenses, note its regulator and then some other details which can somehow reveal a scammer. It's so terrible that today we can invest our money and remain without anything just because some people play on our trust and ready to do anything for their profits.