If a doctor or mechanic was wrong, at least you’d have an inkling that things were wrong and you’d be able to sue them. Whereas with cryptography, no one has ANY IDEA WHATSOEVER if there are back doors until they are used to rob people blind. In all of the cases you mentioned, victims of those abuses have recourse whereas in cryptography, if things are wrong, they often CANNOT be patched and it’s even exceptionally hard for an expert to prove what went wrong.
This is the understanding ANYWHERE. How do we know there aren’t back doors in our OS’s? We literally have no clue. We do THE BEST WE CAN using the clues we have.