|Keep your cat inside. There is no reason for a cat to go outside.
I have to agree with most of the advice you have been given, although I have to say... I might just neuter the cat. The guy has no proof you did it, and when you take it in, you could say it was just a stray. Therefore there really is no evidence, you found a stray cat running around, you caught it, you neutered it. I doubt he would even notice the cat's testicles were gone.
But that's me.
As for the statement I quoted that statement is a matter of oppinion. There is no real reason, disease aside that a cat should not live outside. Although we call them "domestic" or "domesticated" cats are quite independant and capable of caring for themselves. They like being outdoors and wandering and catching things and getting into trouble.
My cat is an indoor cat, my biggest worry [although he is microchipped] is that someone would take him "Aww what a cute cat!" or that someone because he is friendly would take him and light him on fire [I've seen photos of someone doing that
] or some other form of torture.
My sister has 6 cats, all of them she caught and altered. They are fairly friendly, but she can only handle two of them [besides petting]. One of the six does enjoy coming inside and hanging out, the rest would go crazy if locked inside. The one who comes inside is the most handleable and he's gotten an abcess or two [he's an old tom cat] and was able to be treated. The rest generally don't get into scraps and are healthy, minus one, Greta, who does have Feline Leukemia. It's also been shown indoor only cats are more prone to obesity, and that male cats are more prone to having urinary tract infections and get blocked up from lack of exercise and what not. There's pros and cons to living in door, or outdoor, but alot of the outdoor stuff virus wise can be prevented with vaccines, abcesses and cars/humans are the only real dangers.