All cases to be put down are sad. The ones that are dangerous are at least, understandable.
The ones that truly suck hard are those they put down because of space issues, or time. Most are totally adoptable, no negative reasons for them to be put down.
One part of the problem is that while the spay/neuter rate for most dogs in the US is appx 70%, the rate for pit bulls is about 20%.
Increasing urbanization and lifestyle choices make dog ownership impossible or highly inconvenient for responsible people. There are thousands of latch key dogs whose owners go to work in the morning, leave the dog alone and locked up all day. When the owner arrives home, too often it's one or two pats on the heads, maybe a five minute walk to the curb. Frankly, dog owners often regard their dog as just more "stuff"—an accoutrement, an iThing, a Gameboy.
Dogs are social animals and physical animals. Dogs are not solitary creatures. People who can not provide the right environment for dogs, should not own one. If the result is more dogs being euthanized, well that's the way it goes.
Second it. I volunteer at a no kill cat shelter and there is cat that is on meds to stay calm.