+1 for having the default be safe, but this will have to be very
loudly announced ("when migrating from 3.3 to 3.4, TLS connections
will cease to work if blah blah").
Some legit sites with proper
certificates still manage to muck something up administratively
(developer.quicksales.com.au has a cert from RapidSSL but doesn't
bundle the intermediates, and I've told their devs about it, but all I
can do is disable cert checking). This will break code in ways that
will surprise people greatly. But I'd still rather the default be
True.