So, lets say those same statements were made while the students were on residency, i.e., they said those statements in a hospital setting in front of other dentists. Should everyone just ignore their statements? Should the students not be reprimanded?
Why not say they grabbed a megaphone and marched down Main St saying this shit? Of course if you change the setting then you change the appropriateness of the behavior. I insist I can jerk off at home but I [probably] wouldn't do it on a street corner.
If someone is reading this exchange and takes offence, do we deserve to be deprived of the opportunity of employment? Yeah, it's kind of public since it's accessible to anyone but we're addressing only one another. Expression of opinions online isn't as cut & dry as spoken conversation but I tend toward permitting expression rather than defending against the possibility of someone taking offence.
I can see where you're coming from but I view them as having made some tasteless jokes in a setting I regard as private, insofar as a reader who wasn't the intended audience could stop reading and go elsewhere without continuing to get spammed by uninvited material . For me, that's eavesdropping. This is very borderline since they were talking about the dentistry that they're studying at the school, but since the school had to cross the threshold of privacy to discover it then no, it's none of the school's business and the school is at fault for being overly nosey.
I categorize it with Walmart shelf stockers being made to take a drug test as a condition of employment. There should be a privacy boundary that institutions can't cross and I think that protection should extend to expression online when of a conversational nature. Even idiots have a right not to be surveilled in private.