Our dogs are not fixed either. People say it's the responsible thing to do, but that's only if you are not responsible enough to keep the dog sin your supervision in my opinion with most people. I am in many groups for dogs, and most the owners are kids and they just do not do what they should do to protect their dogs and keep an eye on them.
Our dogs have never been in a situation where they may impregnate someone elses dogs. They are not kept somewhere where they can escape, and they are leashed anytime we go anywhere, even if there are no female dogs around.
Some people just find it easier to fix them though... i personally have seen many dogs fixed, and their personalities change, and I fell in love with my dogs as the are
