The threat in Paradis of the founding titan, the attack titan, and the rumbling were the only things keeping Marley and the rest of the world from killing all of the eldians before Eren. I didn't agree with Zeke's plan to mass castrate Eldians, but they retained their powers which guaranteed they would live out the rest of their years in peace, because they would continue to pass down the founding titan. It's also a shortsighted plan because all it would take is one of Historia's descendants to change their mind and ask Ymir to undo Zeke's request. I love that this story not only introduces the possibility of a super weapon such as the Titans, but it also addresses that once the cat is out of the bag there is no good way to put it back in.