This doesn’t follow to me. In the context of the film, Luthor is dead wrong about Superman. Whatever his birth parents’ attitudes may have been don’t enter into it. Luthor hated Superman because of his alienness and his superiority (the latter being his primary motivation, as Luthor flat-out admits — it’s jealousy more than anything truly ideological). But as Jonathan says, it’s Superman’s personal actions and individual choices that ultimately define who he is.Then within the world of the film...
Lex Luthor was right? And Superman has to completely disown his birth parents, who in every previous incarnation had been just as vital to him as his adoptive parents, in order to have his happy ending?
That's still pretty cynical to me, absent any real world implications.