I vote @MelasLithos for Reef Ambassador!
Hi, I see this quite often, and I do believe that most of the time, people just don't know and never thought about these subjects.
I am lucky that I speak three of the most common languages in the world, and like to strike up conversations on the boat (there was only once where I was not able to communicate with my buddy because of language issues). And I do not hesitate to tell people when I see attitudes such as you describe. Most of the time, they will tell me that they didn't realize the issues it was causing/didn't know about, thank me for mentionning it and will try to correct it on the next dive.
Of course, I will never start with that. I would usually start the conversation discussing what we saw, favorite dives, etc. And usually, at some point, I will say "BTW, did you noticed that you were doing this and that?". More often than not, the answer will be "No". And I like to frame it as a discussion more than a "lesson". What I prefer though is point their act to them while they're diving, so that they realize it.
For example, a few month ago, on the third day of diving with a group of people, with went on a muck dive. A young women was flutter kicking very close to the silty bottom, with all the mess that that entails. I gently grabbed her and asked her to watch behind her. When she saw the clound of silt, she had a movement of surprise and immediatly went a bit shallower. After the dive, she thanked me and told me she didn't realized how the bottom could be so easily disturbed.
So I believe you shouldn't be worried about discussing their attitudes with other divers. I know that here, in Asia, where I Iive, a lot of people didn't have the same environmental education and awareness as we had in Europe for example. But they are eager to learn and discuss. Of course, I always try to stay polite and humble when I do that, and it usually goes very well. And it's usually a learning experience for me too in cultural differences ^^