It becomes a political issue when all companies start engaging with it, especially when they do so under external political pressure ("We really don't want to pass a law - how about you self-regulate?").
Consider the situation in Australia, where all ISPs acted in concert to block websites. It's technically not government censorship, but the effect is the same - so any utilitarian rationale behind restrictions on government censorship should apply here equally.
Or maybe this should just be considered a form of illegal cartel.
I'm going into nitpicking rabbit hole, but the definition of 'censorship' is government censorship. The word comes from Roman republic position of 'censor'.
"The censor was a magistrate in ancient Rome who was responsible for maintaining the census, supervising public morality, and overseeing certain aspects of the government's finances."
https://en.wikipedia.org/wiki/Roman_censor
When its not government censorship it's called self-censorship or something entirely different.
