I think the issue comes with unknown unknowns. Before Fukushima someone might have said the same thing you just have, but a new disaster still came along and caused a lot of issues. I am still bullish on nuclear, but I think waving away concerns might do more harm than good.

Fukushima was a known risk though, they just never bothered to fix the problem. Plus just being planned in the 60s meant the initial design was born only about 15 years after nuclear power was invented. Fukishima was like driving around in a Model T, being told original brakes and tires and lack of seatbelts were unsafe, but still being regularly driven down busy roads without bothering to upgrade those features.

Unknown design flaws in old nuclear power plants wouldn't be fixed in new nuclear power plants, unless if by chance.