Shlishi: I believe R’ Schachter has said that it is a very serious issue because if Metzitzah is only for the health benefits then it should be an Issur D’Oraisa Bizman Hazeh on Shabbos because our doctors say there is no Sakanah if you don’t do it. (Maybe one could think like the Tzitz Eliezer and say that if Chazal declare something a Sakanah that it stays a Sakanah L’olam Va’ed even to be Mechallel Shabbos over it even if our doctors say there’s no Sakanah, but that is very, very Shver). Pashtus in many Poskim is that it’s only because it’s a Sakanah if you don’t do Metzitzah. Which makes what to do on Shabbos a very serious Shaila.
Nisht: I was talking in a broader case and not even about Metzitzah. And it’s not so true that people know not to do MBP when they have an open sore. I remember a Rebbe of mine (who is very, very Chareidi) told us that when he looked into this 30+ years ago (this issue has been around for 200 years now) a lot of the Mohalim he spoke to knew scarily little about germs and transmissions of diseases and stuff like that and that of course they would do MBP even if they were sick. Hopefully the one good thing that comes out of this whole controversy is that all Mohalim will hopefully know not to do it if they are even the least bit sick or if they have an open sore.