Personally, having been born and raised in a christian family but later realizing I don't believe in any of that shit, and leaning towards satanist views on life... Saint Peter thought of himself as being unworthy to be crucified in a similar manner as Jesus.
I know my views are definitely "unworthy" and unorthodox for any "christian" person. Many people were born into christian families. Thus, "I gave up on my faith, am unworthy of Jesus and am okay with that, delivering a message contrary to yours. Oh, and I piss on your naïve ideologies while doing so."
That, and then there's the logic of inverting a symbol to signify a message opposite to the original meaning. Which many christians think of as an outrageous symbol, as not every christian is catholic nor well-versed with the symbols of their religion.
Also the "actual satanic cross" you mention is the symbol of sulfur, which will not attract the attention of any christian (which you want to do if you want to criticize your religious community and their double-standards).
Honestly like how hard is it for edgy kids like you to comprehend this