The intent of fading downvoted comments out seems to be to make them more annoying to read than most users would be willing to put up with, and far easier to simply skim over and ignore, regardless of their quality (even when they're not faded enough to be illegible - the fading provides the visual cue to the casual reader that "this isn't worth your time.")

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.

[0]https://gist.github.com/kennethrapp/5b5e413220afb93c9c93