Mary is just a mindless sex doll, only the dimension of sex is important to her, it's when time they can fuck her, she has no real feelings, only lust, Sathoshi was raised differently, accepting this, would mean, losing the respect of his family, he is honestly, he should never, ever, accept his uncle into his life after all this. Sathoshi deserves his freedom, while Kendo and Mary, their lustful life, without respect for anyone, are practically the same, for them, they are only interested in personal pleasure, at the cost of trampling on anyone, and that's what they did with Sathoshi.