When you bring up the topic, the debate can be heated.
Opinions usually fall under two categories:
A) It works.
B) It doesn't work and people are turning their animals in in record numbers because of it.
I pick answer C - neither is true in our experience.
We passed mandatory spay/neuter here in Los Angeles in 2008. What are my feelings about this? It's not working. I am in the schools every day in various neighborhoods throughout Los Angeles. Neighborhoods that I know were the target of this law. Guess what? It's been almost five years and most people don't even know that it's a law. We send flyers home - English and Spanish - and for most parents, it's the first they are hearing of it. Those of us who volunteer in rescue and work in rescue knew about the law as it was ushered in with great fanfare. The neighborhoods that it was designed to curb the constant flow of puppies in? Not so much as a whisper.
I have heard it said that the Los Angeles shelter numbers are up because of this law, which always makes me chuckle. Nope. Shelter numbers are up because people aren't making commitments to their animals. It's a convenient excuse to get rid of that outdoor dog when your home is in foreclosure and you're moving into an apartment. We are an extremely pet friendly city. There are more apartments that take dogs than ones that don't. WAY more. Easy to find. For the first few years, several organizations were offering to pay that security deposit. But no one wanted the money. They just wanted to dump the dog. When you offered them the money, they came up with other excuses - well, he's not housebroken (good news, we can help with free training), yes, but I'm allergic to him so even with free training and the housebreaking taken care, I really can't keep him; we can't afford to feed him (good news, here is a list of food banks and organizations that will give you FREE food and feed your pet for you to keep him in your home), yes, but we're moving and the apartment wants money for a deposit (good news, we can help you by paying the security deposit), yes, but he chews everything and I can't afford to have him chewing them furniture (good news, we have a trainer who is willing to help you), yes, but I'm not home enough and it really isn't fair to him to be alone so much...and so on and so on. This is why the intake numbers are up. Some people are just never going to make that lifetime commitment no matter how easy you make it on them, they're always going to find a reason to get rid of their pet. The economy makes a good excuse for most of them right now.
No one in these neighborhoods is giving up their pet because of mandatory spay/neuter. They aren't doing that because they don't know about the law. It isn't being enforced. While the idea behind it may have been well meaning, it was completely unrealistic in a city this size. Our programs got cut so the low cost and free spay/neuter became hard to come by - how can you make this mandatory if people can't pay for it? We send handouts home with the kids letting parents know that it's now the law and pointing them toward the dwindling resources we have in this area. But no one is knocking on their doors to make sure it is done and the local shelters still tell me that the main reason for giving up pet is 'MOVING'.
While not everyone we encounter wants to fix their pets (some like the money that it brings them twice a year when the dog has puppies), the people who do don't know where to turn. If you're struggling to feed your family, a four hundred spay bill for your fifty pound pit mix isn't going to be anywhere on your list of To Do items. Low cost or free spay/neuter needs to be available and readily accessible. People need to be educated - and then allowed to decide which choice is right for them and for their pet.