I am playing right now and I just noticed when I was viewing messages I got the option to erase them. It was great I got rid of some of them, now I can't find that option again.
You can erase your own messages, wasn't aware you could erase other people's. Maybe you got mixed up about the two? Or maybe you know something I didn't.
I'm pretty sure you cannot erase other peoples' messages. May have been a glitch, but you should only be able to rate up or down other peoples messages, not delete them.
Wow, it must have been a glitch. So weird I was definitely erasing other peoples messages, about 3-4. It was really nice to be able to clear the area for summon signs.