As detailed in the comments, the default behavior is undesirable for us
because we can't really predict all possibilities of exceptions that may
be raised - and thus putting str(e) in the http response is potentially
insecure as it may leak some unexpected sensitive information that was
in the exception.
As a hypothetical example - KeyError resulting from some buggy
some_dict[secret_string] call would leak information. Though of course
we aim to never write code like that.