I share your concerns about criminal brokers / bankers.
I also know the way I deal with the situation will not work for everyone.
I consider my margin account as just another trading tool. So, twice each month I take the profit out of my account.
My account value always stays about the same give or take a few dollars.
My account wasn't large enough to do this when I first started trading so withdrawals were out of the question. It took time and patients to get to where I could pay myself. I know this could be difficult for anyone with a very small account.
I would hate to loose my margin account but at least this way I get paid to trade until the crooks take it..