if every site let you play with bonus with rules that you can cancel it whenever you bust your bonus without sacrificing your original deposit. all gamblers will do this all over again. The result of your actions is solely done by yourself. it is clearly stated (there's a warning before bonus cancellation) that you will have the "x amount" of deduction from your balance. how is this possible for you to blame the site?
This.
If you got such a profit and cancel without reading I don't see why to blame the site. With such profit, just start to make a lot of bets without increasing bet size on loss. You would just lose the house edge and will end up with still a huge profit.
If he just played on the bonus and cleared it, it would be a good site.