I have to do that enough that I'm thinking I might just write a bookmarklet to automate the process.
Downvotes are nothing more than another kind of participation in the discussion and should be treated as such.
Participation is a constructive activity. This is more like graffitiing over someone's comment to make it invisible. As far as I'm concerned, that's shutting him out.I may be misunderstanding you, or missing something obvious, but I just highlight faded comments with my mouse (or finger if on mobile), works well.
It's similar to the reason text posts are faded by default - to make those posts more annoying to read the longer they are, in order to discourage using them as personal blog posts.
If you don't particularly want your hand held like that and are capable of reading more than a paragraph at a time without suffering mental exhaustion or ennui, you may well find these practices to be condescending and passive-aggressive.
I have a userscript that I use to unfade everything[0] and have showdead on and I find that neither has negatively affected my experience much. Although of course everyone's mileage may vary.
Downvotes are nothing more than another kind of participation in the discussion and should be treated as such.