You want unpopular? I'll give you unpopular. No-kill animal shelters are ultimately more harmful to animals than kill shelters.

Instead of euthanizing one violent or chronically ill or old or otherwise unadoptable animal, you spend your limited space and resources keeping it alive while you turn away a dozen perfectly healthy and well-behaved animals who could have been adopted but were instead let loose on the street or were euthanized elsewhere.

Even euthanizing otherwise adoptable animals is a net positive, because there are more companion animals in need of homes than there are homes willing and able to take them in.

As long as it's legal to make your animals make more animals, culling their populations will remain an ecological necessity. Which brings me to unpopular opinion #2: it should be straight up flat out illegal to own a pet that isn't spayed or neutered, no exceptions. I don't care if you think your munchkin cat's fucked up tiny legs are cute. The state should be able to seize your animals and have them fixed with or without your consent.