They won't, they never have, and probably never will visit us as intelligent beings.
I'm very much open to ideas like panspermia, other than that I'm very sure about aliens not ever having visited us.
For the future we're not interesting (yet) enough for a higher intelligence to come visit us.
The resources on our planet are abundant in the universe, we as a species are self-destructive, and we have no real power to fear or covet.
There just isn't any justification for another intelligent species to spend the resources needed to visit us.
Oh and if an alien race wants to use us as slaves, why not build robotics ones that, don't whine, die, starve, or get sick.