For me, it's very possible to be raped by my boyfriend/husband/etc.
We are free use, we also have a safeword.
To me the safeword is a communication tool like any other communication he might get during sex. It communicates that I don't think I can take any more. He may decide 100% of the time to stop when I feel that way (which I'd guess is fairly likely). But in the short term, I'd be okay with him deciding I can take 5 more spanks, telling me that, then doing it because that's what he thinks is best, and that's not something I'm gonna die from.
This also works because if it was something medical I wouldn't likely say "safeword", I'd say "fuck fuck my wrist fuck", and if I'm passing out I can't safeword anyway, so it's not really applicable to those scenarios. In the case of normal PIV, blowjobs, and the "standard level" of bdsm we do, yeah it would be really hard for me to feel raped, because none of those things are really traumatic if it's a situation where I don't start out in the mood, but I get in the mood because I want to please him.
Anal is a bit of a different story - if someone is crying in pain during anal that means there's a decent chance you're doing some level of actual damage (which can also build up in the long run). There's a difference between discomfort and "not okay", and I don't think a good man would ever want to put their partner in that "not okay" space. And in general, I've read some stories, erotica and the "was this okay?" type on the bdsm subs, where it doesn't really matter to me whether she technically said the safeword or there could've been a miscommunication - there are certain ways you just don't treat someone you love.
In the long term, if I feel like my opinion isn't being considered in his decisions at all, that will break trust. It's still rooted in consent, I'm not going to stick around if it's just selfish or malicious. From one day to the next, the consent might not be there in the PC sense for any specific act, but "consent to the relationship" needs to be maintained overall. And he cares that I enjoy sex, he wants me to be eager - neither of us would really like if I was always just "grinning and bearing it". I think a big thing that's missing in a lot of these posts is the reciprocal responsibility from the man: I trust him with free use, because I trust he won't abuse it.