If I was debating or even considering the ethics of sex with a student I would expect people to get upset, yes. It would require a severe disconnect from reality for me to think that they wouldn’t.
Musk followed up the initial tweet (from a third party) by tweeting a page from Roth's dissertation, in which he wrote that services like Grindr (a gay dating app) should proactively develop online safety policies because it was very predictable that gay teens who use the internet might attempt to use the app. 'Underage people might use your adult dating app, so you should plan ahead for that' is not promoting the idea of underage people using the app any more than 'buy a fire extinguisher for your home' is advocating for arson.