A good way of thinking about it can be how children are usually put in cribs overnight. It’s done to keep them safe and generally not considered abusive. Crates, too, should only be used for times when a dog is going to be sleeping or happily (!) playing, chewing on Kongs and other toys.
It is not okay to leave a dog in a crate longer than a few hours during the day, and many people pick too small a size. Your dog needs to be able to fully stretch out while lying on his side. It’s also very important that the crate is lined with soft bedding and the dog is patiently taught to like his crate. This is abusive. This is good.
My Lab is an adult now, so he spends barely any time with the crate closed up. However, he does go in there voluntarily whenever there’s people over and he’s had enough of being social. It’s his quiet place, and I don’t allow anyone to disturb him in there.