I disagree that liberals are more petty than their counterparts. Take for example, Donald Trump. I've never seen anyone more petty than he is and his tweets prove that.
This argument uses an equivocation for the word "friend" implying that a 'facebook friend' is equivalent to a real-life acquaintance.
Un-friending someone on facebook that you don't even interact with in RL, is not the same as "dumping a friend over politics."
Dumping a friend is small potatoes after one has already dumped his / her country.