All very good points and I completely understand. Candidly, that Furlex currently on my boat and the way it's setup look to be very cruising-focused for the next year or so with family. And - most of this years budget? Going to virtually all things that likely make the boat more comfortable vs. faster! So, I can completely appreciate the appeal and your points.
I guess I just don't see that it makes much difference in the end and I always err towards choice and flexibility being a good philosophy. Honestly, if someone has a nice carbon-laminate main and makes poor tactical decisions or doesn't handle the boat well, the advantage is likely neutralized anyways. ;-)
The main material allowed will not make or break this class which is a testament to a great design and people involved with the class. And, that in itself is a cool thing about the J/30 and why we chose one too!