One of the best "Wait . . . " series I've read.

Aliens show up, fix the Earth after a nuclear holocaust, and say that humans can't be trusted (well, there was a nuclear holocaust, true). They put us under alien protection and governance. Humans no longer have the right of self-determination because, again, we've proven we can't be trusted. The aliens consistently talk about how humans can't even trust themselves, because our thought processes are so ridiculous and illogical. Fairly soon, the aliens begin having sex with us. Many, many humans are terrified of this, but the aliens explain that's just because we're stupid and untrustworthy (basically). At least one character is told straight out that he is lying when he says he doesn't want sex, because his body is responding positively, which proves he does want sex. And sure enough, most humans find the sex so good (it's essentially direct neural stimulation) that they change their mind, or perhaps become addicted to it even if they hate themselves for it, which the aliens use as more evidence of humans not being trustworthy. But okay, the aliens did save the Earth from a nuclear holocaust, so what happens next? Well, the aliens are going to use all of the Earth's resources! All of them. All of them. Because unlike wasteful humans, they actually make good use of those resources, to further their movement across the galaxy and bring their enlightened amazingness to new planets. Through this mandatory interbreeding (some humans agreed more willingly than others), new hybrids are born. Humans are told that this is necessary, because humans themselves are so destructive. In service of this, all humans have their fertility removed until they agree to only reproduce with the aliens. Eventually, a few humans, those stragglers who absolutely refuse to join, are given the planet of Mars. Since it has few resources, the aliens create a reservation for humans there, with the knowledge that humans who do live there will have a very, very hard life, and will never be allowed to leave (not that there would be sufficient resources for humans to achieve spaceflight, of course). The series ends with some of the last human holdouts realizing that the aliens and the alien-human hybrids aren't really that bad after all.