Thank you for posing that question! I think the tendency to blame Russia/China/whomever is a complete failure to address the actual root of the issue.
If everyone who works for a non-American intelligence agency suddenly lost the ability to post on the internet, would Americans start getting along better? Or would a significant percentage of Americans still have a reactionary hate fest running on their televisions every waking hour, their opinions reinforced by Facebook echo chambers full of other actual Americans? I think the difference would be so small as to be imperceptible.
When it comes to tearing each other apart and working against our shared interests, America has a well-oiled machine running that hardly requires any foreign intervention.