It is a bad idea because "mute" is not necessarily used punitively by users. If I mute someone who is extremely active in my feed, it does not necessarily mean I consider them spam. It means that I don't want to see what they're posting at that moment. I frequently do this, and then go back and unmute them later, as a means of managing my feed. If my mute suddenly counts as one-of-x required marks toward someone being considered spam by such a relay, then my mute suddenly becomes punitive instead of the way I intended it. Amethyst behaves similarly to this and it is one reason I would never use it.