It would be great if externalities were insured by everybody, yes. But externalities are real, why would you ignore them "out of fairness"? The sane thing to do is to consider them for all kinds of power generation, and then make the best choice. Nuclear just has huge unconsidered negative externalities, we haven't even yet talked about cost of storing and guarding waste for centuries.

Thankfully there are only a few more years until wind & solar will have solved this once and for all by being cheaper, externalities considered or not.