Your scenario is valid. It comes down to three opinions, which in your perspective (as Person C) break down as follows:
1) What person A wants: To share content with people whose opinion he respects
2) What person B wants: To comment on content he finds interesting
3) What person C wants: To read and contribute to commentary on content he finds interesting
Let's look at it from Person B's perspective:
1) What Person A wants: sycophantic praise for tired, tedious content
2) What Person B wants: the right to call a spade a spade
3) What Person C wants: Person B's commentary on Person A's content
Not so rosy any more, is it? Now let's look at it from Person A's perspective:
1) What Person A wants: To share content with people whose opinion he respects
2) What Person B wants: To watch the world burn
3) What Person C wants: To read and contribute to commentary on content he finds interesting
It becomes clear that Person C's wants and dreams are fairly constant in this universe, while Person A and Person B's wants depend a lot on perspective. Considering all three perspectives are valid, and considering that commentary often matters as much as content, there's no obvious way to resolve the situation. BUT:
Without Person A's instigating the discussion, there's no discussion at all. There's no content. There's no conflict. And if he can't share content without being free of Person B's hassling, he's not likely to contribute. This is, after all, a site founded on following individuals, not subjects. You can block people on Twitter, you can block people on Pinterest, you can block people on Tumblr, you can block people on Facebook.
So in theory, Person A's interests should overrule Person C's.
HOWEVER it doesn't work that way.
Person C can shout out Person B. Person B can now comment on Person C's shout-out. And Person A can do fuckall about it.
Problem solved. To the detriment of Person A, I might add.
So I'm not sure what your objection is.
mk, correct me if I'm wrong.