The Cain Apologist believes that RDM (and company) has stacked the deck against Cain, hitting us with lurid accounts of her atrocities divorced from their contexts, and, in so doing, jettisoning the show's usual sophistication. CA's are chafed by the aura of relative goodwill that has decended over Roslin and Adama in the wake of Cain's appearance; they complain that in pitting Adama and Roslin against Cain, RDM has made the pair too unambiguously heroic. Some CA's even entertain speculations that Colonel Fisk is a Cylon trying to sow discord in the fleet - or they believe that Fisk is a man moved by frustrated ambition to lie about Cain's command.
A number of Cain Apologists are people I respect on the whole - but I find I must part ways with them on this particular issue.
On the matter of certain speculations: You can technically classify Fisk's conversations with Tigh as hearsay, but we quite unambiguously saw Thorne attempt to rape Sharon, we quite unambiguously saw a psychologically broken Gina with angry, red welts on her thighs and back, and we quite unambiguously saw Cain look upon Gina with utterly no sign that she was troubled by what she saw. Cain knew how her prisoner was being treated by her interrogator - and he was being deliberately cruel beyond anything we've seen on Galactica. (Compared to continued sexual torture, anything done to Leoben was downright merciful. I certainly hope we can all recognize the difference here, even while we decry torture in general.) Moreover, we've seen her display open contempt for the uneasy alliance Adama and Roslin currently maintain between the military and civilian colonials in their fleet, we've seen her wield her military authority like a sledgehammer, and we've seen no sign that she understands she's betraying anything by throwing her power around in this way (an understanding that has been shown to be present with Adama and even Tigh, though they, of course, have also abused their power to some degree). And lastly, it is surely significant that while Adama is planning a surgical strike against Cain's command, Cain hopes to take out the entire Galactica CIC. In light of all of this, I find Fisk's accounts pretty plausible. If they turn out to be definitively true - or, at the very least, they are never contradicted - I will not be surprised. The pattern of behavior I see on screen doesn't really throw doubt on the possibility.
Unlike my dear friends, the likelihood that Cain is just as maniacally fixed on military victory as they say does not trouble me. I think selenak has it right. I believe RDM intends for Cain and the Pegasus to serve as a warning - to stand as a dark mirror of the Galactica. Everything that Cain has either definitively or allegedly done stems from impulses and tendencies we have seen on Galactica - but Cain, unlike the Galacticans, has taken those tendencies to extremes. Cylons - even the human models - are "toasters" on the Galactica just as they are on the Pegasus. They are not considered worthy of trust or tender, loving care. This prejudice comes from something legitimate, mind - we must not forget the whole attempted genocide issue - but exactly how easy is it to go from this legitimate hatred to wanton, almost animalistic, cruelty? Saul Tigh can't stand civilians as a general principle. How easy is it to go from this attitude to openly using/abusing civilians for military purposes? I believe RDM wants us to meditate on these types of questions. The presence of the monster challenges us to draw the line. I plan to explore Admiral Cain in my writing in the future - to explain her reasons and put together the psychological building blocks - and I plan to do so with these questions in mind. That she appears to have become a monster - a consummate predator - does not make her any less interesting to me.
As for how Cain's presence is changing the relationship between Adama and Roslin, I have a little more faith than the CA's that the conflicts between Mom and Dad are not simply over and done. This is a moment intended to highlight that, differences aside, Adama and Roslin are both colonial patriots - and I believe we need moments like these sometimes to add urgency and tragedy to the moments of disagreement. In music, dissonance evokes emotion because it ultimately resolves to a consonant chord - you feel the music pulling you towards the pleasant harmony. Storytelling, in my opinion, can work the same way.
I don't know if I've made myself clear or not, but there you go. As in all things, one's mileage may vary.