Are you talking specifically about items belonging to the satanic cult or finds that are evil?
There are many finds that one could deem evil that we collect.
For example, I never thought I would find something like this in Canada, but I did a week ago.
WWII German Belt Buckles - MilitaryItems.com
Now, many would say the Nazi's were evil for what they did. I'm not even sure if I can post this find here.
I know if I put it on fee-bay, the auction would be terminated immediately.
I could say why but that wouldn't be politically correct. Lol.
I'm keeping this buckle as it has that "coolness" factor.
You could say war is evil and yet that is one of the biggest interests among relic hunters.
I'm big into the fur trade and yet what those traders did to the Natives was bad.
What the missionaries did to them in the name of religion was pure evil.
Slavery is evil and yet the slave owners were good religious folk.
Find a slave tag and you will make the banner instantly!
People find KKK items and collect them. Another bunch of religious people who did pure evil.
Many who find such items keep them because of it's history, plain and simple.
Even though I think a lot of what I mentioned was or is evil, I'd still keep those finds. I find them fascinating.
As for upside down crosses, I wore one in the '80's for a short period. It came with image of being a headbanger!
I still like 80's metal.

Cheers,
Dave.