“Cattle rustling is illegal. I would assume that kitty rustling would be, too.”
The central question is, “Are the cats private property or not?”
If not, the taking of cats probably should be incouraged, given their rather negative impacts on the habitats they infest.
PS Google the Toxiplasmosis issue, before you keep cats around. If the researcher is right, the “Cat Persons” are crazy, and they caught it from their cats.
Plus we have the well known problem of children being attacked by packs of feral pit bullcats.