Partisans gonna partisanate.
Most folks I see posting on FB are pretty partisan liberals and they think I'm a hard core conservative. In A51, I'm considered a hard core liberal. I'm OK with all of that.
Humans are very tribal obviously, it's just a lot easier to be part of Tribe R or Tribe D than to sit and ponder each issue individually.
There even is a Tribe "I", folks who claim to be nonpartisan and independent thinkers, but usually aren't. Being a nonconformist is just a conformist who conforms to being non, in their mind.