And there it is. “We can’t”.

You want to know the difference between those who want to see us head out to the stars and those who want to stay put?

Those 2 words. Says it all.

He said we "can't...with any currently-existing technology". That is absolutely correct. He did not speculate on future technologies.

I worked on an atmospheric Cerenkov detector for my grad work. We measured -among other characteristics- energies. We cannot at this time shield against particles of those energies. And organic tissue would not fare well with bombardments of those energies (TeV).

Well...we can shield if we start digging. Hard to take a cave into space, though. Albaby mentioned a moonbase. It would have to be sub-lunar. Not sure how many meters, but I would guess at least 10 meters. Otherwise the inhabitants would get their DNA shredded. The few realistic designs I have seen for such an installation usually had the water tanks above the habitation to increase shielding.