Yes, but you're not talking about Bitcoin, you're talking about a Bitcoin fork. Bitcoin wasn't designed to let users provoke a fork with the GUI, that's how your Bitcoin fork BU was designed.
So much for Honey Badger, it seems bitcoin might have a serious flaw, if what you are saying is correct.
Much cheaper than a 51% attack. Just spin up a handful of non-conforming nodes and mine an invalid block. Boom! And Bitcoin is done for.