Hi. I know it is an old thread but I'm writing this for the future reference. Yesterday I bought used bike. Today while I was cleaning the bike I have noticed some thin, line like wear inside of non drive side of chain stay. First I tought it was epoxy or nail polisher applied to hide or fix small crack (my imagination). Then I realized the wear is at same place where the tire "hairs" rubbing. Then I started to search if it is possible, and I have found this thread. So yes, it could be bad for the frame. In my case the the paint varnish has worn out where the chain stay is concave, and the aluminum of the frame is visible where the chain stay is convex. I hope my english makes sense
I wish to attach pictures but it has message count limitation.