My view is that the bookies write the rules. If they choose to write them in such a way that I can make a guaranteed profit then it's only good business sense to take that. If they don't like it then it's entirely within their power to change the rules (not offering bonuses, for example).
When you make the rules you play by then you can be accused of exploitation. When someone else makes the rules then it's a loophole.
The only way that we cheat them is that we are not "recreational", but then that's open to interpretation