It will be hard for people to vote for better politicians, so long as those politicians who are allowed to represent an existing party have to be selected by the party itself.
Corbyn catches flak because despite loudly proclaiming how straight talking and honest and pure he is, he refuses to disavow Marx (rather: dodged a question asking him to in a classic politician style), and praised Fidel Castro, both men whose ideas and policies caused profound suffering on a massive scale. That rather implies that if Corbyn ever got anywhere near actual power he'd rapidly start abusing it.
Mandatory reselection after boundary changes should see to that.