I think the main reason I dislike the incest thing is because it's being compared to being gay and the thing is...I don't believe in one true love. Even if they're adults who are madly in love, so what? They aren't allowed to marry one specific person. They might even break up and marry other people for completely normal compatibility reasons! But if you're gay, you can't be with anyone, ever. No matter who you date, it'll be gay so you're expected to die alone. That's a completely different scale than not being able to marry your brother so you'll have to date literally any other guy.
Additionally, the maid was willing to murder people and support her brother murdering people. Even if I was desperate, I wouldn't support my girlfriend murdering people not to legalize gay marriage, but to get us out of the country to get married somewhere else. She should have broken up with his ass and dated other people. Which she can do. Because she's not gay, just in a bad relationship. Or even just skipped the country without the murder. I can't believe leaving the country is that impossible. They were just afraid to do it without help because they had comfortable lives. The brother at least deserves the death penalty honestly (in-universe, I don't generally support it irl) and the maid should at least go to jail if not get the same. So yeah, waste of a reward to plead for them.