Well yes if you believe that all MP's should back the Leader of the Labour Party and have no independent views of their own.
The point is that principle would apply whether the Leader was Blair, Brown , Miliband or Corbyn, SURELY! It's either a 'principle' or not.!
Where would the idea in the OP fit with Corbyn and McDonnell who were happy to not back the Leader of the Labour Party time and time again themselves? Wouldn't that be a case of hypocrisy .
The word 'democracy' has been banded about as a 'brand' for Labour under Corbyns leadership yet the idea proposed in the OP would hardly be democracy in action, more like 'do as I say, or leave the party'. How is that remotely democratic?
Actually I don't think there has been a more dictatorial, threatening abuse of democracy so openly shown by suggesting Labour MP's who were elected by their constituents have to 'put themselves up for reselection' .
The narcassism behind that if it was a dictat is astounding.