If you take the idea that suicide is a rational, meaningful form of protest, then like the nazis you would want to prohibit the people you're murdering from killing themselves first. The nazis were sadists who wanted the act of murder all to themselves, so they overlooked the existential aspect: The dead can't talk either way. Frankl at least wanted to keep them alive, to prove that existence did have meaning, even in the worst suffering. So? He was a humanist and they were nihilists, and you think that amounts to the same thing?