Two other options I've seen are either fading out the text. For example: on a site with white background, black text, it fades out the text to a very pale gray on the selected comment. You can still highlight it and read if you want, but otherwise your eye skims over it.

That might be tricky here, due to widely varying journal styles.

The other one is to auto-collapse or auto-hide a given comment (again, might be tricky here.) People can click to reveal it. Again, tricky here, because larger comment threads auto-collapse, so it would be hard to tell which one.

However, I mention in case someone has a brillant idea that'd solve those practical difficulties. I like the overall idea of being able to de-emphasise/make harder to read offensive comments without making them invisible quite a lot.