I think part of the reason Kaysar's actions were more acceptable than Jennifer's was because Kaysar stupidly handed her HOH in exchange for her promise not to put him and the rest of the Jedi up for eviction. Eric & Kaysar had an agreement of a sort, but didn't make a bargain to seal the deal. Jennifer made her promise in exchange for HOH - it just seemed like a bigger betrayal since it wasn't a blatant swap - you let me have HOH and I don't put you up for eviction.
America also doesn't like Jen because of her attitude. She seems to be immature and hold grudges. She claims the decision was her own, which means that she obviously was not playing strategically.
Also, Kaysar played the game, but didn't make it personal. He appears to be trying to let it go, whereas Jen just keeps on making faces and rolling her eyes.
No problem with Maggie winning. She definitely threw at least one HOH to Ivette as part of her strategy - thus avoiding being the one to have to vote off a friendship member when Janelle won veto. She was overbearing, but her play had an influence on the final outcome.