I don't get it either. Our shelter dogs were always crated overnight since they weren't allowed in the bedrooms and they would go there when it was bed time with no problem. Occasionally they'd go to their crate to take naps or seek refuge there during storms. I guess if a dog willingly going into a crate to sleep while everyone else slept is cruel and abusive I don't know what they'd think about actual abuse. Our dogs lived long happy lives. Most dogs I know have a spot that's tight and cozy, maybe even covered, that they go to; crate or not. If you crate train with positive reinforcement it's a benefit for everyone IMO even if you don't make them sleep in there.
You're talking about the dog not minding being in the crate since you've taught them its nice and cozy. In that case why does it have to be a crate, why not say, an indoor doghouse?
As far as that goes, there's nothing wrong with that and that's not the part that people actually have problems with (but it's a nice strawman to argue against).
The part that is cruel and abusive is locking them up when nobody is at home so they can't damage your possessions. If there is some emergency like a fire, intruder, something falling down, etc, they can't do anything about it.
I think what we did is much more similar to what you describe, with the crate door left open, so she didn't feel isolated when the other pets and humans were in other rooms. we moved the crate upstairs and left the door to it open, and she took a liking to it as her own space, and would choose to go sleep in it like it was her bedroom (or whatever), but having it at the distant end of the house clearly alone for the sake of isolating her is what I found counterproductive.
