If it would have been specifically centererd around the physical pleasure, I would have 100% agreed with you. However, beom was always treated like an animal since his childhood, so ofcourse, it comes as no surprise, that he lacks the skills of verbally convey his emotions because of which he resorted to the physical expression, but atleast, the master could have talked and explained things out verbally rather than giving into beom's instinct.
There is no problem in having rough s** with your partner & that does not make the relation toxic in any way, but, using s** as a substitute for communication is absurd & tbh not hot.