This is actually a good point. You'd think Halbrand's plan at this point would be rally the southlanders. Galadriel isn't a big deal to them, but if he's their king and helps them out, they'd likely ignore when the 'knife ear' lady comes by and says their king is evil. Maybe give them some rings with power to help them defend against Adar's orcs.
Heck, since Galadriel is so afraid to tell people the truth (and its clear he knows this as he taunts her with it), Halbrand should be rather free to operate as he pleases. If he's being kind and helpful, Galadriel is stuck trying to undermine a helpful person without explaining her reasoning.