Nice post Showy but I don't think it's necessarily a childish thing to want a physical marker to assist with the mental filtering we all do.
Some of us might find it harder than others to deal with large amounts of information; this is a peculiar weakness of mine, I can't process things very quickly, and thus having a paperclip or a sticker or something to keep my paperwork in order in everyday life is really important (though I often fail to do it)
It's the same thing; some have a remarkable ability to remember everything and everyone. People often comment on threads in the manner of 'I remember your posts from last summer when you had that argument with your mum' or whatever - I'm always baffled as to how they know, particularly when there have been namechanges in between.
I can't do it. Therefore a visual reminder, in the form of a colour or something, well, yes it does feel slightly distasteful but OTOH it would be quite useful.
I'm not thinking of applying it to everyone I ever disagree with. Just those who are maybe on my' suspicious' list, those who post continuous reams of political bollocks stuff and the conspiracy theorists, who don't warrant a ban, but are nevertheless really blimming annoying.
Plus sometimes, just sometimes, I do want to lock someone in a metaphorical cupboard, because I know I might say something I regret unless I do.
By and large I agree with your sentiments though. I wish there were a way; perhaps there isn't a good way. I feel like MN is just too big and too scary for me these days.
So I should probably just leave.