There is a lot to be said for those who oppose TNR on moral grounds, i.e., feral cats live a short and sometimes brutal life and they deserve better. I think this is a universal wish by rescuers, and those of the general public that actually think about it--which are many.
We all wish they all had homes, but sometimes just the massiveness of the problem and the suffering makes all of us wonder whether we are not just chipping away at a granite mountain with a toothpick.
On the other hand, many who oppose TNR are those who just don't like cats or bird-types, or nature freak environmentalists that think native species are more important than cats, donkeys, wild horses, etc..
Lots of "experts" from CA Fish and Game provide lots of irrelevant data that supports their opinion that unhoused cats should be captured and killed.
They content TNR does not work because people dump their animals at colony locations.
They ignore the fact dumping will always take place whether there are colonies or not, and cats will always be getting lost. It is estimated that 5% of the housed cats become strays each year. TNR has to cope with that steady influx of animals as well as the non-sterilized cats already in the colonies.
Personally, I think the only real solution is to prohibit cat ownership. Those who already have homes can stay with their owners for life. Most people do not deserve to have cats, dogs, rabbits or turtles. They don't deserve to have children either.
TNR could continue on the unhoused cats, and the numbers of incoming cats would decrease each year, meaning TNR would become very effective.
I might say the same about dogs, rabbits, birds, turtles, etc.
Only special people should be allowed to have animals, but there is no way you can legislate certain people to have them and others not.
Why should so many animals suffer when only a smaller percentage of people (maybe 25%) can really afford to take care of their animals, and also have the heart to take care of and share a life with them.