If legal authority or lack thereof is not the issue then the details matter if we're going to make an issue of this. I suspect that the researcher's private communications should not have caused them to be denied entry, though to be certain we'd have to see them.

Would a researcher who said something like "J6 should have gone all the way" have been denied entry in 2021? I suspect they would have, and that many would have cheered that refusal.