You must live an unusual life to have witnessed so many shunnings from so many various Christian denominations, most of us have never seen a single "shunning" from a Christian denomination.
Many, or even most non-Mormons married outside of their own denomination for instance, and we never even heard of "shunning" until we read about Mormons.
Don’t you find it almost amusing that so many mormons know all these “things” Christians do to their members and if you say “what” they accuse you of being blind to your own denominations.
I have seen churches split of really stupid stuff and still get together for pot lucks once a month or so because they are all still brothers and sisters in Christ after all.