(Kaiba's attitude is really something they only see among the severely mistreated, and his reaction just confirms what they were already sure of.

They also know that he cares about more than just himself, because they've seen his memories.)

Irrelevant: that those you care about are familiar with your attitudes does not invalidate Turing's point. Additionally, regardless of their acceptance, allies in your universe of origin are unlikely to be pleased if you return damaged or, should death come to exist here, fail to return entirely.

(How would Mokuba feel if you just disappeared forever Kaiba? Especially if you died because you were an idiot and made an unnecessary enemy?)

You do not care about nonphysical harm?