Both atomic bombings, the Daigo Fukuryū Maru, and the Fukushima disaster come to mind. Perhaps a better question is why wouldn't people with a personal connection to Japan be wary of nuclear contamination? Or 'why don't the rest of us?'

Certainly there are some people in/from Japan who are enthusiastic about the future of nuclear energy. But I think it's fair and reasonable to say that cultural trends exist and a randomly chosen person with a personal connection to Japan is more likely to be critical of nuclear energy than a randomly chosen person from the rest of the general population.

As the only nation attacked by nuclear weapons, Japan tends to be anti-nuclear.