Regarding showing dishonesty - yes, but "supporters of X are dishonest" is "ad personam" - that's poor argument.
Better to use hypocrisy to show "even supporters of X don't really believe their view is right, so it probably isn't".
Still, not a good argument.
Their view could be right, whether they do really believe it or not.
E.g a politician could say "don't steal", and he could be stealing himself. That he is hypocritical about it, doesn't mean stealing is "probably" right.