Sometimes? It depends on the severity. I have learned that many different people have various determinations of what humane means for people, let alone animals, and they do not always match up. I do not think it is a black and white answer, and what may be okay for one pet may not be for another.
(Some people consider it inhumane to keep a large dog in an apartment or to not walk them constantly, for example, but not all dogs have the same energy requirements. My own Alaskan Malamute is more than happy to sleep most of the day away on her memory foam bed inside, but by that definition I would be "abusing" her.)
More on topic, this sort of gray area informs my beliefs on virtual pets. I have no reason to look at the MFP small pets and assume abuse. Beyond just pretending they get let out, they quite canonically leave on their own adventures and send you a post card along the way unless you turn it off. Further, these are not real pets that you can see the suffering. If there were some sort of detailed suffering mechanic, you bet I would avoid it, but why would they add that? It is the Sims. A virtual dollhouse. You abuse the pixel people and pixel pets no more than you abuse Barbie when you change her clothes without her permission.
