William is doing what a lot of famous people do - using their access to the listening world to offer any opinion.
That is always a two-edged sword.
In order to have reached a level whereby you have that level of contac, you have already created a situation where you are going to be vilified for your views, whatever they are.
A lot of famous people who are in that situation speak out on their personal views, clearly believing that the flak they get is worth their efforts to influence something that they feel is important.
Credibility in this situatio is everything.
Prince Harry has none whatsoever, mainly because he seriously over-estimates the importance of his views in the wider scheme of things, added to the hypocrisy of his lifestyle.
Prince William has a considerable amount, and is sensible enough to be careful how he uses it.