Dammit, phone just lost my post!
Sea's post about 4 back crystallised in my mind what I was trying to get at when I said non-BDSM traditional romantic fiction can almost be more dangerous.
BDSM and rape fantasy fics are often about what their authors call "hurt/comfort" (which incidentally isn't necessarily even sexual - our fave male character can get horribly wounded in battle and the side kick can provide comradely emotional comfort), or what is known in the BDSM community, I believe, as "aftercare". The problem is that this mirrors the abuse cycle in DV - violence, fake apology, period of being nice to make up for it, gradual ramp up in tension, more violence and repeat. I suspect the neurotransmitter/receptors and psychological sense of addiction to the highs and lows are the same in both instances.
But there's a sense in which romantic fiction as a whole does the same. Instead of the hero attacking the heroine, he demonstrates his dominant nature by fighting off the bad guys. And often, the bad guys are attacking the heroine, which serves to underline her submissiveness and/or vulnerability. It's the cycle of abuse, but at one step removed. The thing that makes it insidious and dangerous is that this isn't how it works in RL. In RL the dominant man who can fight off the bunch of blokes on a Saturday night punch-up is the same guy who goes home and beats his girlfriend. Violence, once allowed to run rampant, doesn't stay compartmentalized.
I've had some interesting conversations with an anthropologist friend of mine about this. Male on female violence isn't constant across societies, it varies. One of the predictors is the level of external threat a society faces. DV is lower in agrarian/peaceful hunter-gatherer societies than in warlike tribes constantly having border skirmishes with their equally warlike neighbours. And she tells me that when you interview the women about their attitudes to DV, it becomes clear that there is a kind of Faustian pact going on. The women will say things like "he only beats me because he cares about me enough to get angry". They see a bit of non-fatal violence as a price worth paying to avoid gang rape and possible murder by raiding parties from the neighbouring tribe. Or as she more succinctly put it - priming male violence to a hair trigger level is like leaving a loaded gun around the house - you never know what direction it's going to go off in.
To me, this plays into the social/psychological explanation that I think Sea and I favour, rather than some sort of evolutionary explanation of the sort posited by Biscuits. It's external threat level which seems to prime male violence, then it goes off unpredictably. And this can vary on timescales much shorter than those needed by evolution. My grandfather, by all accounts, was a horribly violent man (mostly directed at his sons rather than his wife - he was emotionally abusive to his daughters). But when you dig into family history a bit more, he'd served in the trenches in WW1 (yes, that long ago, I am an old gimmer, and the youngest daughter of an older mother who was in turn the youngest daughter of an older mother). He came back with PTSD, which probably explains, though doesn't excuse the violence.