I know this thread has moved on slightly from the origional post, but I do think class based analysis has flaws. I think you can be a feminist without subscribing to class analysis theories. I think making sweeping statements about men does invite others to make sweeping statements about women, which is something I think feminism and feminists should challenge. I think it is possible to explain ways in which men as a group opress women as a group do not have to be phrased this way.
I am also not convinced that the post the OP is refering to was actually meant in this way.
I do think statements such as "All rapists are men" are different.
I would say some rapists do "get off" on raping women. Some rape is about power, but to me, with many rapes, often those where the rapist is known to the victim, I am not at all sure that at least some of the motivation does not come from sexual desire and arousal.
In some ways, I feel the "rape is about power" arguement can be unhelpful, as it allows men to distance themselves from rapists (and women to distance themselves from those who commit sexual assult). If you make rapists into a homogenous group with a charactaristic, and you do not share that characteristic, it helps you convince yourself you could not possibly be a rapist.
Also, even if rape is about power, what is to say that the men commiting the rape do not gain sexual pleasure from that power?
I would suggest there are probably as many motivations for rape as there are rapists, and it is unlikely, given rape is a sexual act, that some of them do not have a motivation of sexual pleasure.