Bow,
I know that you come from a very different culture with different practices as most of the people here. Pretty much all of us believe very strongly in spaying or neutering pets for many reasons.
First of all spaying or neutering greatly increases their life expectancy as unaltered animals are MUCH more likely to get cancers (uterine, testicular...). Not only that but there is a HUGE problem with overpopulation of pets in our countries. Spaying and neutering is simply the responsible thing to do. It helps control the amount of innocent animals that are put to sleep everyday.
Try looking at this site
www.petfinder.com It's full of animals in shelters that were bred by accident or by people who didn't know what they are doing. It's because of these animals that you are met with so much passion from our members.
Yes, many of them come across quite strongly but most of us volunteer at shelters and try to help these animals as much as possible. It hurts us to know that more dogs will be brought into this world who will most likely not be guaranteed homes and will suffer and die prematurely.
Tell us about your country and how you deal with the pet population. What happens to the animals without homes there?
Another reason we promote spaying and neutering is because it makes the life of the animal so much easier. They are not always in trouble for hormonal behaviours they cannot control (humping, running away, and other erratic behaviours). They don't live their lives trying to get something they can't have.
The animals don't miss something they never knew.