The letter says: “We know that high inequality undermines all our social and environmental goals. It corrodes our politics, destroys trust, hamstrings our collective economic prosperity and weakens multilateralism. We also know that without a sharp reduction in inequality, the twin goals of ending poverty and preventing climate breakdown will be in clear conflict.”
Correct, you don’t, because those are garbage disciplines based on nothing whereas economics is decidedly not. Economics is the study of constrained choice, using rigorous math to model these scenarios and applied statistics to test the models. Any 1st or 2nd year course you take in economics isn’t revealing truisms about the world - they are introducing concepts and highly simplified, abstracted models so that when you get into upper year courses and you start using extremely heavy math to make more realistic models that are serious attempts to explain actual human behavior, you’re not completely lost.
You take at face-value that certain subsets of economists argue in favor of bank bailouts but against student loan relief is proof that they’re evil, or garbage, or bought and paid for, without even understanding the arguments. The bank bailouts were loans which the banks paid back - would you be fine with the government giving out more loans to pay off existing student loans?