This is a good point, and it doesn't seem to me like an "ignore this user's comments only for replies to my stuff" thing would make too much sense, either. Hmmmmm.
I'm aware that I'm perhaps atypically vehement on this point of view - I refuse to delete old phone numbers, and have had a tough time removing frenemies/old flames/former friends on Facebook and other social media simply because, although I may not have a connection to these people now, I'd prefer to know what they are up to if I so choose. Except in extreme cases (a particularly poisonous former friend, a particularly painful and frequently-thought-of old lover) when I can't help myself or it's better to excise the drama, I opt for the ability to have knowledge over completely cutting someone out. Part of this is because I want to prove to myself that I am able to not interact with them (once a relationship is ended, for instance). And a large part of it is also a raving curiosity I've always possessed. I very well may be in the minority here and if it comes to that I will accept it, but for me the mute function would lose its functionality, unless in an extreme, inescapable case of personal harassment.
Yeah, I can see where you're coming from, because I probably wouldn't use "mute as comment ignore" all too much either unless it was blatant spamming. I personally wouldn't use the mute function as it currently is either because I don't want to block someone from sharing their views with other people, even if it's views I disagree with on posts that I make. Social media is hard, let's go shopping.