The concern is, Aragorn, that the backbench hardcore Brexit bunch are ~20 MP's. Currently that is the grand total of the majority. When there are 100+ more, then it may be easier to ignore their concerns.
This is worrisome, as I have a sinking feeling this sabre rattling is all a ploy.
That said, Comrade Corbyn being sent back to the political wilderness is always a net positive. Some quotes from his shadow chancellor may demonstrate why this is so necessary.