High tax = brakes on = slow growth.
Slow growth = less well off, less money to spend on public services.
Stimulating growth and improving public services with more borrowing is OK provided the level of debt is not too high. We had the highest deficit of all major developed countries in 2010 and a debt mountain spiralling out of control. Borrowing more at that time would have been madness. Something had to be done. And raising taxes any more than even a modest amount would have crushed any hope of a recovery.
I understand this is an unfortunate truth for people totally pissed off with the state of our public services, but nevertheless it is the truth.
Corbyn's plans would provide a short term boost and then very quickly turn the economy into full speed reverse. By the end of his term, the economy would be in deep recession and debt spiralling once again. Count on it.