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The "politically" seems to be implied.

This rhymes with when people say “it’s just politics.” What does that even mean?

Facebook is totally okay with people being influenced to buy things, but doesn't want to be seen to sway their non-consumption-related opinions.

More like 'without paying us first'.

Oh, I doubt that. I imagine they don't want paid propaganda, either, since that'll make them appear complicit, politically.