The "untestable" meme is just a thought terminating cliche. It's as if you believe no researchers ever considered the brilliant insight that the framework is difficult to test. History is littered with plenty of examples of a novel discovery, understanding, or technology yielding new opportunities for experimental design.

It's also a glib dismissal of the unexpected mathematical elegance of string theory that makes it so compelling. Worse, it completely ignores the material contributions to applied physics that string theory has made possible which is obviously worth "spending your life's work on" - as if people need to justify the value of their life's work to disinterested onlookers lest they be demeaned.

This is a pretty silly belief to hold about science. Plenty of strong, well held standards of the modern era were considered ridiculous fringe beliefs a century ago.