Neutering Dogs

Well look at what I was just looking at! Neutering male dogs! You have to be real mature to read stuff like this because most people would laugh since it's talking about a dog's dick...And as I was reading this, I just felt horrified! Why would they cut that...part off? I wonder if it'll hurt. People neuter dogs because of overpopulation. But that's a pro because we don't want an overpopulation of animals. But then again, the con is that what if it's the last of its line? Like, maybe all that one type of dog species will die out. Do they keep the testicles or something? -.- Like seriously. If I had a male dog, I'd keep it AWAY from a female dog so they wouldn't have sex...But then again...What if it can't help itself? Oh god! I'd have an unwanted litter of puppies in my house. But maybe I'll give them to my friends! Problems solved...
   Do people neuter cats? They should do that to all the strays...I'm seeing cats everywhere now that it's scaring me actually O____O