Honestly, I think it varies.
Let's assume that after Chute posted the thread about mental health awareness and suicide prevention, and there's a bunch of very positive, supportive posts - and someone decides to come along and give an opinion something along the lines of:
lol just dont be a pussy and stop crying imagine being so weak and seeking attention like this on the internet lol
It's not helpful. Chute's post says that people's words matter. And they do. In this particular case - you're essentially suggesting to certain people who may already feel unsure about approaching someone regarding their mental health that it's not okay to feel depressed, or sad, or alone, etc. They may just be words, but sometimes people don't understand how vital words can actually be.
Generally speaking, like I said, it varies on what the opinion is. If it's not so much an opinion as someone just needlessly slamming other people, then again, it's probably not conducive to a healthy discussion. You have to be willing to actually talk without resorting to saying "This person is a piece of shit" or something along those lines.
However, if the opinion is valid, and offers someone's genuine thoughts on an issue and it simply counters what a forum moderator might have as their viewpoint, then yes, it would be abuse to remove that opinion.