I can understand why people wouldn't want Regina to be with Emma, but I don't think in the same vein that people okay Hook's actions. "When I jab you with my sword you'll feel it," it is not a romantic gesture. Hook left Emma and her family and associates in an inescapable prison. He called her "dried up and useless."
Emma and Hook's meeting was finding him under a corpse and him lying about his identity. Hell, Hook was willing to leave everyone to day AGAIN in season 2 by sailing up and only by Regina/Emma's actions they saved the town. So, I don't see how Hook abuse of Emma could leave to romantic entanglement and not Regina. To me, Hook went from one obsession (trying to kill the DO and failed) to another one (pursuing Emma when she really didn't give off anything to express interest when she is trying to save her son).
I'll doubt it since there is already a handsome male character that has murdered children, sold them to Peter Pan, and talked abou thow he used drinks as tactics to sleep with women.