> "This waste is dangerous for the next 10,000 years." "Holy shit! We need to build a high-tech underground fortress to contain it!"
Time is a major risk factor. Look where we were 10,000 years ago. There is relevant chance that 10,000 years in the future no one will easily understand the danger of radiation anymore, so we have to prepare for that possibility.
You seem to have missed the other half of the point I was making, which was that there's lots of non-nuclear hazardous waste which lasts forever and we don't get nearly as upset about those.
Time is a major risk factor. Look where we were 10,000 years ago. There is relevant chance that 10,000 years in the future no one will easily understand the danger of radiation anymore, so we have to prepare for that possibility.