I actually think that cats are better off being spayed and neutered. It's healthier for them: did you know that female cats that are NOT spayed have a larger risk of getting mammary cancer? I adopted one of my cats when she was 2 years old (and she wasn't neutered), the more times they are in heat before they are spayed means the greater the risk of getting cancer. She developed tumors 4 years later and shortly after passed away.
I also believe that it's humane to have them neutered, otherwise they spend time each month in heat. I don't think being in heat is a fun or comfortable experience for them. There is also a huge cat overpopulation. Why would you risk bringing more cats into the world, when thousands are killed every day (even kittens) because nobody wants them.