Let me put it differently. Mech is a browser emulator. How sensible would it be for a browser to quit on 404s? Mech is a subclass of LWP::UserAgent. How sensible is it to change default behavior radically? Both are obvious mistakes.
This particular change was supposed to help new users, one imagines, but Iíve seen this question come up constantly since it was made: What the heck is going on? My script just quits!? And for adept users it broke all existing scripts and forces a new line of code in everything. I love the functionality of being able to put in your own code ref in but having it be the default is a mistake: conceptually, historically, and expectation-wise.