Huh... can't say I ever anticipated running into someone who would seriously put forward the claim that slavery might be better than voluntarily working for pay...
Slavery, which is to turn people into personal property, is an abomination. Even the ancients described slavery as "unnatural". In certain situations, however, it might be preferable. You don't deliberately leave your bike out in the rain. But you would if your bike was responsible for keeping itself out of the rain.
Don't take it out of context, OP is saying that at one point in time in a particular place, slavery may have possibly been more "secure" or reliable as far as having food, water, and shelter.
This is in no way excusing or apologizing for slavery or saying eh, it wasn't so bad.