In my early days of interest in this, and when the internet was still young, I found a chatroom in one of the IRCs and talked to several women there while it was active. Probably where my interest in this grew just knowing about it through one woman, and it became a fantasy of mine based on the details many here now shared with me of the act. But also talked with some new women to the room that were ashamed. At that time it seemed women started this by accident, forcefully mounted or drunk/stoned with a partner and then playing with the dog. Those especially that were forced by a dog were feeling shame not able to fight him off, being overpowered, scared when he growled and entered them and afraid of what he might do to them if they fought him off. But then there was more shame after, partially that they had just had a dog inside their body, but especially because part of them enjoyed it and thought that they were a freak. One woman there expressed a lot of those details to me having had her dog force her down and afraid of him, and also feeling freakish for realizing after that she enjoyed it. Like the others here said, if no one is being forced, you assume the position, and he accepts and mounts, then why not both enjoy? I told her this as I comforted her mind a bit. A few days later she was back and said that she had initiated the act, and was much more at ease, able to let herself go and enjoy it more fully knowing that there were others and she wasn't a freak. She'd share her adventures over the next few months as she got more active with him and in the chatroom, where she ended up being one of the greeters for other newbie women and comforting them.
So know you are not the only one, and it's been going on for years. Maybe it's the internet, but I suspect there are even more these days and seems now less are forced or under any influence, they are willing partners and wanting and searching for it. I actually find that the hottest aspect now, a fully aware and willing woman, like you and many of the others here.