I am pro-spay/neuter. The average pet owner out there just isn't capable of caring for an intact dog of either sex responsibly and properly, therefore, I feel it's in the best interest of most dogs out there to be spayed and neutered.
That said, there are also people out there who are more than capable of having intact animals. They seem to be few and far between when I'm out and about in public, but they are out there, and in those cases, I don't really care.
I don't understand why anyone would not want to spay their girls though. It's messy and inhibits regular daily life for at least a month a couple times a year generally... and in my experience, they always seem to come into season at the most inconvenient times. I'd much rather spay and be rid of all of that. Pyometra scares me like crazy too.
And after living with Ripley, whose hormones get in the way of his focus pretty easily these days, I can't wait to neuter him one day as well. He's a good dog, but his constant (almost obsessive) want/need for sniffing and marking and girl finding (outside only, but still) is really annoying. I'm fully capable of keeping him intact forever, but I have no desire to. Of course I don't let him get over the top about things, and a lot of it is just his age, but it still gets in the way of training when I'm constantly having to get his focus back to me.