Not so much opportunistic but unavoidable. He's a slave to the powers surrounding him, and the more real-world power he attains the less choice he has in how to wield it.

The real gut-punchers of how his station is betraying Paul's actually and genuinely good character are going to come in the second book, that is, subsequent movies.

And, yes, Paul, the Atreides in general, are good people. Noble, honourable, just, wise, kind, upright, everything, to a fault. Which is the only way to tear down the Messiah archetype, the Messiah has to fail despite their virtues, the failure has to be dictated on them by the universe, in a way that's not incidental but an unescapable truth about how the universe works. Or at least humanity.