Hm... They may actually. It depends on the side to look at this situation from.
Abusing from the point of funds can be natural to poor quality brokers or even scam ones. They can easily cheat on clients, while decent brokers tend to ensures high quality conditions and only then impose some minor charges which serve as "salary" for a broker.
It's not bad, cuz the broker provides you with an infrastructure and access to the market, while you give it money in the form of fees/spreads/swaps. It's honest, and usually they don't charge a lot. It's okay.