If I see a person nazi regalia I might feel uncomfortable and I’ll certainly judge them for their choice of clothing, but never would I advocate for making nazi regalia illegal.

There's a bit of a difference between a religion, and a regime that, in its ten years of power, managed to kill tens of millions and start the largest and bloodiest war of all time.

Surely most religions have a larger body count over the years than that, if that's the criteria?

Well, because populations have grown so much in the last two hundred years, to the extent that a sizable chunk of all lives ever lived are after 1800 or so, I don't think that a long history in pre-modern times would move the needle that much.

Also, the Nazis are just really exceptionally bloody-handed. In terms of intentionally, directly killing people, they killed like 16 million people. In terms of intentionally, indirectly killing people, their deliberate use of famine killed eight or nine million civilians in the soviet union alone. Then you add all the people that died due to massacres, or were killed as collateral damage, and you can understand why 30 million people died in the USSR, the vast majority of whom were civilians. It generally gets much worse in areas the Nazis had a longer duration of control: in Poland, they killed about one in five people.

It's generally pretty hard to kill that many people before the 20th century, because the means of killing are too innefective, and the number of potential victims is too small. For what it's worth, Genghis Khan is probably the most bloody-handed pre-modern figure, so if we're going to blame religion for his behaviour, it's probably shamanism that has the highest death toll.