The "everyone has to agree" rule is true at our house although it has only applied to political signs. But at our house it's "we all have to agree that we actively and positively support this candidate, none of us is just voting for this candidate grudgingly because it's the best option available to us," which feels very different to me from "I'm afraid that I'm moving in with a right-wing troll." Do not move in with a right-wing troll. Also do not move in with a person you can't have the "all in agreement" conversation with, but..."I'm afraid of what flag he will fly" says to me that this person is probably spending social occasions desperately worried of what their partner will say to their friends, which is no way to live.