coerce someone under threat of divorce to participate. If lack of activity X is truly the tipping point for the BS, they have every right to divorce.
I just never understood why a sex act in and of itself means so much.
Nearly everything that happens in early R is "under threat of D" to get the WS to participate. Shoot, that's what the 180 is all about, showing them what they will be losing. Going NC, timelines, telling the truth, all of it is said, something directly, usually indirectly with "or I will D your cheating a**" at the end of each request/demand.
To your second paragraph, I'd say, respectfully, that's because your not a man. This topic has been discussed at length before, and it divides very neatly down gender lines. The reason you don't understand is because you probably know that you could have your H do anything you want with you in the next 10 minutes if you so desired. He'd never deny you any sex act you dreamed up, or, speaking for myself, that's how I was with my W. Of course it wouldn't resonate with her, she's never been denied sex or sexual acts by me, and perhaps not in her entire life. So it's just very different between the sexes here, IMHO.
Flip it. What if it involved a WH and not a WW. And the BW said “Since you fucked that slut, I’m going to put on this strap-on. Bend over and grab your ankles. Or, I call my lawyer and it’s D and I’ll take half your assets, your pension, the house and full custody of the kids. But I’ll be kind and give you one week to get comfortable with having this 12 inch strap-on shoved up your ass.”
Abuse or not?
Well, first off, did I do it with my AP? If so, then no, I don't see that as abusive at all. Especially if my W had expressed interest in it before, I'd denied it to her, and then went and did it with the AP (and this is the situation we're talking about most of the time here, H asks for anal, W says no, gives AP anal on 2nd date then continued to deny H anal that's what often sparks and fuels these threads).
If I didn't do it with the AP? No, I don't see that abuse, I see that as an "option". And let me tell you, if I were the cheater, and my W had a desire to do that (NOT to hurt me, because she was really into it sexually), I'd jump at the chance to take Mr 12" in my nether regions to prevent a D. Losing my W, losing my financial security, my home, my family; it would hurt a LOT more than anything you could possibly do to my rear end. People do that every day for fun, gay men do it all the time, not to hurt each other, but because there's obviously something enjoyable about it. I'd bend over and look at it as a new experience with the person I loved and try to figure out what I personally enjoy about it. Because there's obviously something to it, otherwise millions of people wouldn't do it on a regular basis.
Now, if we go one step further, if she wanted to beat me with a broom handle, or something that was only designed to inflict pain, I'd probably see that less positively. Yes, the pain I'd feel from a good "code red" style beating would still be a fraction of the pain of losing my W, but I'd be concerned about her motivations. People don't hit each other like that for pleasure, they only do it to inflict pain. And that would scare me a bit more, because it meant that my W really wanted to hurt me, not explore new things sexually together. I'd probably do it, just because the pain of the broom handle would also be less than the pain of D, but I'd be a lot more conflicted about something that was only designed to hurt me, not please her/me/us.