The illegal immigrants aren't staying in your home, they're staying with whomever they're paying rent to. What right do you have to tell him who he can rent to?

Good question. If he also decides not to rent to black people, certainly, that’s his business, and I have no right to tell him who to rent to. Correct?

If you're asking me personally, then yes it's none of your business what he's doing with his property. If he's not renting to black people, that means more tenants for people who aren't racist to rent to. But that aside, housing discrimination laws are based on the moral principle that people should not be treated worse based on their skin colour. Upon what moral principle is the notion that people should be treated worse based on their place of birth based?

Treat your neighbor like your brother? Nationalism and before that tribalism are as old as our species.