the thing people need to understand is that dulcie is, put simply, #problematic. (the hashtag and associated connotations are crucial, here.) this is, without question, a good thing for her character. i see dulcie as the kind of selfish that toes the line of acceptability. sure, she's guilty about it sometimes, but she still follows through. the meaning behind her name, ripped from don quixote, is (in muir's own words) "a woman you want to exist, but really doesn't." that isn't just referring to cytherea! dulcie herself is emphatically not the person anyone wants her to be, with the possible exception of cam and pal. and they definitely had to learn to be exceptions; the only question is if they succeeded, and if so, to what extent.
i firmly lean toward the interpretation that cam and pal did in fact fully comprehend some of the more unsavory parts of dulcie's character, and if anything only liked her more. as they should! how boring she would be, if she were perfect! hell, if she were not #problematic in some way, she would have drawn very clear lines regarding her relationship to them. that proposal would never have been sent if dulcie hadn't been wonderfully, charmingly selfish enough to leave the possibility open.
that's actually part of why cam and pal didn't catch on fast enough at canaan. dulcie would have been hard pressed to not think gideon mooning over her was hilarious, to not go along with it. she'd tease gideon plenty, in ways that she really shouldn't; she'd just also be pulling strings to get gideon to realise that it's harrow she actually wants. in the scenario imagined by cam and pal, where dulcie has cut them off to soften the blow of her death, it wouldn't be out of the question for their dulcie to entertain herself by meddling with the ninth disasters. nor would it be out of the question for dulcie to cut them off in the first place, because unlike cam and pal, dulcie isn't predictable. she doesn't follow a strict internal code in the way they do. she can do things they can't, including shitty and spontaneous things.
dulcie's selfishness, her love of ugly unfinished things, and her *humanity* are exactly the influences cam and pal needed. the sixth are a pair of ridiculous near-superhuman prodigies bound by duty and morality. they need someone to make them worse. to keep them human. it's this influence paul still needs to stay in check.
dulcinea septimus is nosy, annoying, messy, vengeful, dramatic, impulsive, and while not quite a cradlerobber, is uncomfortably close. and i love her so fucking much. and so do camilla and palamedes. and so do you. i'm not giving you a fucking choice