Actually, that's pretty much covered in-universe. The kitchens of Hogwarts are full of house elves who can pretty much make magic into their gimp-suited bitch, and are pretty much slaves themselves. They'll even hop-to for any student that happens to find their way to the kitchens, which, IIRC, is a convoluted path precisely for that reason. (Enough that any student that figures it out is left unmolested for the most part, as they'll have earned it.)
As for the issue of house elf slavery... Well...
As for the issue of house elf slavery... Well...