Okay this is a serious question for all the guys out there that put their own dick pic as their profile picture....and then try to find a woman to chat or meet. Do you really think women like this?
As a guy, I don't like this either. However, it's not the picture per se I don't like, but the attitude that goes along with it. As somebody else here said, some women also use pictures of their breasts or genitalia. But in the majority (although not all) of the male profiles that do this, the person seems to have an aggressive and entitled attitude. I agree that the picture
and the attitude impart a negative reaction on the part of most viewers who don't belong to the same group.
As for why this is, I put it down to a certain cultural upbringing that lacks subtlety and an awareness of others. In some cases it probably works right away—attracting the attention of the kind of person who is not put off by it. (And, in fact, maybe that's the point.) But when it doesn't work right away, and I suspect that's most of the time, it will never work at all; in fact, it will cause an immediate negative reaction that's difficult to counter.
I've used the avatar that I do here on many different sites over many years. I don't provide a picture of myself for obvious reasons, but I also want to use something that's somewhat unique and artistic. (It's a painting by Gil Bruvel.) While I might be turned on by the subject matter on this site, and while I might want to gain the attention of some women who frequent this site, I have my own sensibilities—and putting genitalia into my avatar would run counter to that.
When looking at the avatars of women, am I hypocritically interested in those with female genitalia? Sometimes, if I'm honest. But most of the time I find that I'm more intrigued by unique and non-sexual avatars. More than that, however, I look to the content of the person's posts and of their biographies. If they have nothing interesting to say, then I generally ignore them. I'm always disappointed by empty biographies—regardless of the avatar.
As you say in your original post, what some people want to do is fine for them. It's just not for me.