In the debate between Scott & Jean, they're both right- her from an in-universe perspective, him from our own.
I mean, it's perfectly understandable to not want to see an entire race to die. But from our own, we know that the Brood will always be what they are because that's the use writers have for them- murder lots of people and the heros stop them. Plus, Jean's solution is ultimately "let's avoid dealing with this for now to see if can come up with something".
Exactly. Scott particularly has been forced into a very out of character mode, although Hickman clearly intended to give him some peace until he fell out with Xavier and co. But since he left early, Cyke mostly didn't do anything.
Proteus is one guy. The Brood are in the millions or billions (maybe even trillions) of beings.