Funny to think of pregnancy as curable, but yes of course that's true. However, it doesn't really change the numbers much.

Also, from what I have read about the early 80's bathouse scene, it is possible that many of those guys did acquire every STD known to man, so at least in that case the sexual transmission route could work even with such terribly low efficiency.

Regardless, it seems strange to label it as a STD from an evolutionary perspective, it doesn't fit that profile, and it seems incredibly unlikely it could have evolved as such.