Hmm, I dunno, I do think "cocksucker" comes in ahead of "motherfucker" on the AE offensiveness scale, male to male. Anyone else, or is that just me?
I'm a woman, so the "fighting words" part of it doesn't come into it much for me, though I'm aware that in some circles it would. I'm not the brawling type. I'm also not going around calling men either of those things to their faces, though I have been known to say that someone thinks he's a badass mofo or some such. I do know plenty of men (blue and white collar, though not academics) who use "motherfucker" for whatever they're annoyed about. This motherfucking bolt is stripped! I had just fixed the bumper when some motherfucker comes along and dings it. I'm aware of the "mother" part of it, but I think in a lot of contexts it's just an intensifier for "fuck" or "fucking" rather than to be taken according to its constituent elements. Sounds to me like you always hear the "mother" as "mother," in other words.
I wouldn't want to comment on the relative social backgrounds of different segments of our military. I couldn't possibly hazard a guess. My general sense, of course, is that -- along the lines of what Lonelobo remarks -- those with other options try to keep out of it, these days. I think tour extensions and crappy working conditions have many who would otherwise have considered it (to pay for college, for instance, or as a fast track to citizenship) thinking twice.
And yes, re: 8, I do think that humor is one of the main places we explore taboos, including swearing, and their shock value. Witness Lonelobo's invocation of Sarah Silverman (whose act is too much for me personally).
@ 12, I think pretty much all surveys are answered by little old ladies. I remember reading somewhere that it was a big problem for pollsters during the last U.S. presidential election because there were so many members of a particular target demographic (18 to 34) who no longer had landline numbers. Kids these days.