What do you mean by "slavery"? The term has been applied to many practices over time. The more egregious forms (e.g. transatlantic slave trade) were justified by "well, they aren't really people, are they?"; tamer forms, like Roman slavery, were justified as institutions, as being a necessary component of the Correct Way to Organise Society. I don't think being enslaved has ever been considered a good thing (except by comparison with alternatives), although I'd be happy to learn of a counterexample. Likewise, being raped is not considered a good thing, except as far as it forms part of an Institution necessary for the Correct Way to Organise Society (e.g. a patriarchy). Each individual instance of rape is regrettable, even in rape culture.

Indeed, you will not even find people defending factory farming, except as far as they defend the institution, which is part of the status quo and therefore necessary for promulgating the status quo. (Usually something about "but farmers will have to change their practices!", as though farmers don't already change their practices so frequently that it's hard to do academic research on farming.) If you want to find something wrong that people will actually defend, in its own capacity, you need to consider examples like bloodsports… but just thinking about what people might say about the topic is no substitute for actually talking to them about it.