Hi, woman here, too. Women can and do patronize other women and tell others that they are "protecting" them by taking away the choices that that group wouldn't make. The patriarchy is not enforced solely by men even though it benefits men.

The argument that you are making falls into that category: "I am not into BDSM and don't understand how any woman could be. Therefore I find it offensive, and since to me, as someone who is not in it, it looks offensive to women, it must be offensive to women. I should oppose it for the sake of other women." Look at the rhetoric of some of the women on the pro-life side of the abortion debate. Look at the women who say that other women should stay home as mothers, or the women who slut shame anyone who has multiple partners, all of whom are enforcing the patriarchy. Your gender isn't a defense for opposing legitimate lifestyle choices. The same goes for women in BDSM, stay-at-home moms, strippers, and anyone else who chooses a lifestyle that would be outside your comfort zone. And while there are women who feel pressured to do those things when they would rather not, that doesn't mean that we can say that none of those are legitimate choices or communities for those who want them. I'm sorry the people you know have been in it for the wrong reasons or have associated with the kind of asshole who isn't really in it and doesn't really play by the rules. The fact is that there's nothing wrong with choosing the BDSM lifestyle just as there's nothing wrong with voluntarily fulfilling any traditional gender roles that make you feel good.

Lastly, you disapprove of an entire community based on the activities of some people who are outside the community but use its name to justify their disgusting actions. That's the exact same thing feminists have to fight when the occasional woman who actually does hate men starts using the label "feminist" to defend herself while stating that men are all terrible, or they can't be trusted around children, or men are all would-be rapists, or any of a number of other actually anti-man sentiments that I've (rarely) seen women express. If we don't like it when people associate us with those whom we don't consider to be part of our movement, then why is it ok for us to lump the entire BDSM community with people whom they don't consider to be part of their community?