I doubt you really think that odds of transmission — or commonness of the disease — doesn’t matter.
On the first point, if I were HIV positive, should I have to tell someone I play basketball with, in case in the course of a game we have a nasty fall together and our bloody wounds touched? No, because the chances of transmission in that case are infinitesimal, and my right to privacy outweighs another person’s right to know of the “risk” they’re taking by playing basketball with me. (The case UT is talking about involves chances much greater than this, but the point is just that odds do matter.)
On the second point, consider HSV 1 (one type of herpes), which the majority of the adult population harbors in their mouths, regardless of whether they know of it or not. If I happened to be aware that I am positive for HSV 1, should I have to inform anyone I kiss, even though they probably already have it too? (Again, UT is talking about something somewhat less common — presumably HSV 2 on the genitals, which only about a fourth or a third of adults have — but the same principle applies, that it’s not a super-simple black-and-white issue.)
For what it’s worth, I have had a thorough STD screening and am not positive for anything, even HSV 1, so I’m not throwing this stuff out there as self-defensive rationalization. I genuinely think it’s a tricky issue, and I think it’s worth thinking about the rationale for why some decent people would not feel obligated to tell a prospective sex partner about being HSV positive, even if they know it — if anything, it makes you realize, even more, that every time you have sex with someone new, you’re taking a risk of STD transmission, and you need to do everything in your control to minimize that risk.