Hint: every broker will do this. If you think any broker (let alone retail) will let the client's risk taking threaten their existence, you are deluding yourself. It's a little bit like insurance: as long as most clients take diversified risks and don't push the system to it's limits, the system works. When a significant portion (majority?) of the clients all pile into an increasingly hairy position, the broker will step in and prevent the clients exacerbating the situation further.