What I can't understand about the Blairites is why the insist on joining the Labour party in the hope they can drive it to the right. Why don't they join the Tory party and try to pull it to the left. Surely that would be better for the country.
Because you've misunderstood the argument.
The argument is about what wins elections and not what's the best policies. New Labour won every election they ever fought. Far Left Labour has lost every election it has fought in 50 years. You can argue all day long but those were the facts before Corbyn and remain the facts now.
People want a centre left Labour because they think doing some good is better than doing no good. I agree with them vehemently.