It's expected of "friends" but is way more shocking when family is the problem.
Actually I kind of see it the other way around.
We can't choose our family--sometimes people are "stuck" with folks they don't really get along with because they are blood or in-laws.
But we can freely choose our friends--it always surprises me when some people choose to surround themselves with people who are not good for them....
Shocking is not the word , emotionally painful and scarring is more appropriate IMO. And yes you can choose to write them off, I have with two close blood relatives. Sad but what they did, there's no undoing.