Because Barr is literally a fascist with a long history of violating civil rights. He wants to rule unquestioned, unopposed, and unaccountable. He doesn't care so long as he can torture into compliance.
https://www.aclu.org/blog/national-security/william-barr-has...
My personal philosophy is civil rights are not up for a debate or vote. Normalizing them is itself a form of damage that mere politeness can never justify.
It looks like Barr has been pushing pretty extreme views for longer than I've been alive :/
I can definitely see why you would use the word fascist to describe him