I agree with the news commentators who say he shouldn't be writing to cabinet ministers, trying to influence policy. However, Putin, invading countries & handing out Russian passports, is behaving like a land-grabbing dictator.
Prince Charles is not the King, yet, so he is maximising his opportunity to say, well, what we're all thinking, basically.
I remember the controversy of the State Visit of the Chinese President. Instead of joining the formal greeting party & banquet, he booked himself to attend a much more minor event in Cornwall, to show his disgust for human rights abuses. The snub was not missed by the Chinese & the media.
Is it unreasonable to be pleased that he speaks out & a bit
by the bad press he's getting for it!