Have you (or your campus Moodle Admin) applied the "Manual message read marking" option? When this is used, it requires the user to mark any post as "read" when they view it (just click the "Mark read" link that appears in the same area of the post as the "Reply" link does).
So, even though viewing a post won't mark it as "read" (remove highlighting) automatically, I find it less of an inconvenience than trying to find one or two posts (among many) that I wanted to return to.
For instance, as I read over the unfolding discussion and contributions from students, I can manually mark those as "read" that I don't necessarily want to revisit. For those that I do want to return to, I leave them as "unread".
The other element is that I can change my mind and mark a post as "unread" after I manually marked it "read" initially.
I do think this is quite backwards, however. The more efficient work-flow for an instructor is to have things automatically marked as read when we read them, with the option to mark them as unread as desired - not the other way around.
But, I can live with this for now. Maybe version beyond 2.3 will see such a change toward efficiency and increased user-friendliness.