Tom,
What are you basing this belief on? Personal experience? Do you know people that work for brokers? What facts/statistics do you have that would help prove your point? Anyone can make a claim like that but without any proof its pretty worthless. Why would a broker want to "Show you the door" if you are paying their spreads? That's how they make their money is it not?
Oh and if this thread is a wind up please ignore the above!!!
I've been screwed a bit by my broker. It's not like i was doing much wrong. The problem is. If they have no way of hedging it fully and it's going to lose them money on average, they will just get rid of you or stop you from doing it. None of my trades can cash settle anymore. Everything must be rolled.