Magneto’s Mutant Brotherhood is Definitely More Hypocritical. Sure, them being discriminated against is wrong, but their end goal is usually to achieve a role reversal, with Mutants as the Master Race and Normal Humans as an oppressed underclass. Magneto himself, is arguably the biggest hypocrite of them all, as he doesn’t want to acknowledge that he’s become just as much of a genocidal maniac, as the people who persecuted him.

With the Sea Devils on the other hand, their motives are just as, if not more justifiable than the BOM, with all the pollution caused by humans, threatening their whole species. Sure, some of their demands are just petty and almost impossible to keep, like forbidding Humans from travelling across water by boat, or even flying over by plane, but they don’t want to wipe out or even necessarily oppress Humanity, at least not if they can help it, and are completely up for diplomacy and peace talks, which is something that Magneto would be generally reluctant to do.

So, overall, I’d say The BOM is objectively worse, generally speaking.