It feels like the Labour Party will be dammed whatever they do. I’ve no idea why Starmer has chosen this hill to fight on, he’s not coming across as a strategic thinker here, just someone who doesn’t want any lefties in the Labour Party. Moreover he is creating an environment where you either agree with him or you’re gone - a dictatorship in all but name. No checks and balances to his folly (which he will have). I guess you need to be in the rose network to be one of his sort.
Be interesting to see how the grass roots view the purge of the left, getting these folk out knocking on doors and campaigning might be a bit harder than he thinks right now. Sure you’ll get some who would vote for a pig if it had a red rosette on it, I guess he is hoping for enough lethargy that only those type of Labour voters bother plus enough “dissatisfied” tories who are happy to vote for Sir Tory Starmer.
As you said earlier we are in a one party nation right now. A strong opposition anchors the government of the day nearer the centre than their ideologies - this Labour Party on the right can surely only send the Tory party further to the right, sure it might make them unelectable but at what cost.