I didn't say it was a 'left wing coup' - I said Milliband changed the rules. That's all I said. The politics don't matter; it was simply a ridiculous decision from Milliband.
The hard left simply took advantage of it. A 'broad church' became a hard left playground overnight.
The problem is Corbyn AND his policies - as I said earlier, they are unmoderated. The policies are popular with the electorate in theory, but the electorate likes to see a realistic plan to implement them. Again, if you asked the electorate "should everyone have £15,000 more a year in their pocket?", that would be a very popular policy too - but if you just run that policy into an election 'as is' then you'll be rightly laughed at.
As an aside to davek and Milkman, Corbyn is absolutely hard left. He might not be as left as those from the 70s, but in modern context he is definitively hard left. Society has moved more to the right and more to the middle class in the past thirty years - as such, 'hard left' is an 'easier' goal to reach politically.