Ok, I understand what you're asking for.
Josephine's method is what I do, too. If I don't read a thread I leave it unread and the red yes doesn't bother me. In fact, I take it as an indication that I have not seen it. But of course, everyone is different in how they use a site and you are asking for a feature to help accommodate the way you use the site, not Josephine and me.
There are actually performance issues related to the marking of hundreds or even thousands of threads as read all at once. Each thread you have seen (or marked as read) becomes a record in the database here that becomes more data for the server to sift through. But that's not a significant issue.
Let me contemplate it a bit.
