For males, neutring is very minor surgery. It could easily be done at home without anathesia. You basically just name a small slit in the sac, squeez out the little marble-sized thingie inside and it heals on its own. Easy as pie and not at all disruptive to the cat - but it sure makes him a nicer boy.
Spaying is major surgery and really doesn't need to be done if a cat is indoors. However, your cat will have a mensus about 2x a year and all of the local boys will want to visit her. Having litters will shorten a cat's life plus the cat population does not need to be increased, therefore, spaying and neutering is for the good of cats as a whole species.
I could probably neuter men too if they wanted it. Can't be MUCH more difficult.
