I am not always a fan of what Prince Charles says when he intervenes in the public policy arena, but people who say he should keep his mouth shut are wrong. As a minimum, as a private individual he is welcome to his views and as entitled to express them as anyone. If we think they are ridiculously biased because he is from the privileged elite then we can ignore him. But generally his interventions seem to chime with the thoughts of ordinary people, and if privilege gives him a platform to speak from then he should, in my opinion, use it.
Politicians do not limit their views to promises made in their manifestos; captains or industry, newspaper editors, senior policemen, trade union leaders and others never feel constrained in using their position to express views, exert influence and impact, not always benignly, on our daily lives. So if any if you don't like what Charles says, attack the argument, not the man.