The timing reeks of trying to sabotage the film. It barely got made in the first place and this isn't going to help it.
Carrey's not stupid...he knew what he was signing up for when he took the role. If he's so opposed to content of the film and he doesn't want to promote it, then he should donate his salary to victims of gun violence. But I'm pretty sure that he won't.
Good luck with your Dumb and Dumber sequel, Jim...a sequel that should have been made 15 years ago. No one gives a fuck about it now.