Regarding the Labour party, the Parliamentary party must (MUST) reflect the membership.
Until this happens there will be no end to the crisis. So the activists need to deselect the ones who are unrepresentative. Painful and unpleasant, but it needs to be done.
The Conservatives also have this problem, but so far we are bit more discreet and polite about the issue (perhaps too discreet and polite - at least the EU referendum flushed out the Remainers).