I'm not kidding when I say this.
It is of utmost importance to have both a safe word and a safe gesture/action. You need to have both. If one partner continues and ignores the safe sign, then it's assault. IMO.
"Willingness" is a grey area; the fact that a woman eventually engages in sex does not mean she is willing.
Engaging in sex,and strapping up in leather and chains are two completely different things (I think). If these woman strapped up and got in character, that's a lot more voluntary, to me, than just taking off clothing and agreeing to have sex. This has got to be a very hard conclusion to come to in the court room. BDSM is a rather touchy subject with people who don't/have never partaken in it (or even know what it is for that matter). I feel like the outcome will be heavily biased based on the age and gender.
There are people that would accuse me of assault, and possibly even rape if they saw the stuff my girl friend and I do. We have three different safety signals, and until either of us do one of the three, anything goes. If someone like me was on the jury, I'd be a lot more likely to at least be willing to hear this guy's side of things. If someone like my mother was on the jury, it'd probably just look like rape no matter how it was portrayed.