There's a difference between being physically strong, having a backbone as you put it, and being a badboy. There are extremely muscular men who are very nice people, and there's also a huge middle ground (into which most men fall) between being a boorish badboy and a spineless pansy.
If a woman has a preference for muscular men, or skinny hipsters, or even fat men, that's fine. We all have our physical preferences. And the fact that women want to date men with enough spine to have meaningful character is a good thing. However, women who are attracted to loud, boorish, and stupid badboys are utter garbage.
The attraction to badboys is not aesthetic; many badboys are out of shape and ugly. I think the appeal of the badboy is that it provides release from the pressure that is put on women to "marry up". It's not looked down upon for a man to marry a woman less ambitious and intelligent than he is, as long as she's good on her own merits (e.g. if he's a Wall Street quant with a 155 IQ, and she's in a lifestyle career and has a 130 IQ, that's fine, because she's still a smart woman who can hold her own in intelligent conversation). Women, however, are expected to marry men with at least the same level of earning potential and intelligence, because of a lingering concern with gender roles and the expectation that the man will be equal or dominant. This obviously places a lot of pressure on high-power women. The appeal of the badboy is that, although he's virtually never intelligent or ambitious, he's dominant on account of his sheer arrogance and narcissism, but at the same time worthless enough that he can be flippantly discarded. This enables the woman to enter a relationship where she takes a submissive role, but one that has an "off switch"; she can leave without pain, since it's unlikely that she'll form an emotional attachment to such a useless and defective man.
[*Edited for clarity @ 12:26]