Lolorito is... a scumbag, but a predictable scumbag. Everything he does is for the sake of profit; even donating funds to the Sultanate is a long-term business move. (Can't make money if Ul'dah falls into chaos.)

The situation surrounding the banquet is... complicated. More likely than not everything played out according to Lolorito's script... until Ilberd cut off Raubahn's arm and goaded him into a fight, sending the Scions into a panic and causing them to flee. Had we stayed behind we'd likely have been cleared of charges... eventually. After Ilberd was kicked to the curb. Minfilia would still be with us, and Y'shtola and Thancred would be no worse for the wear. ... maybe.

A Dark Knight in Ul'dah probably wouldn't last too long, since they'd likely go on a killing spree not long after getting there and be cut down by city guards. Or they might take a more pragmatic approach and only go after the worst of the worst; despite the corruption in Ishgard, Sidurgu is content to deal with only what he can see (Ystride during the 50-60 line) instead of prowling the streets and looking to punish evildoers... though you do this during the 60+ quest, it ultimately leads to a different tangent.

Amusingly enough, Musosai from the SAM 50-60 line acts almost just like a Dark Knight, wandering the land and bringing justice to corrupt elements of society. Fortunately Momozigo stops him from cutting down the culprit(s) of the Ul'dahn quest, but who knows how things might have turned out without him...