> Why are some aspects of US law declared beyond the scope of acceptable discourse?

They're not, it's fine to talk about these things, and there are plenty of places where people discuss all aspects of law around sexual offending.

The wrong time and place to talk about them is when your organisation is discussing potential problems because a high profile person linked to your organisation has been accused of raping a coerced child. People in that thread needed a useful way to deal with "MIT has links to Epstein, and Minsky is accused of raping a child". RMS's diversions into "is it rape?" and "is it assault?" were not helpful to that thread.

Either RMS was oblivious to the distress and distraction his comments would cause, or he knew and didn't care. Neither is good.