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.
