There is a serious problem in the front tail output shaft gear (the 17T one). It was designed as a fuse so it will evaporate 9ms after the tail impacts on the ground. This annoying feature will generally save all four crown gears and also the lower 80T gear. Disgusting if you ask me. Its much more cool (although more expensive) to replace all four crown gears and maybe the lower 80T gear plus going through the orgy of setting up the mesh again.
... end of sarcasm
Now back to serious and to answer to the OP question... if, and I mean "IF" one of the crown gears would lock up in mid flight (never seen it or hear it happen) then the front 17T tail output gear would strip and basically let the crown gears jammed. It would never possibly allow the crown gears to eat themselfs up. I think your friends are confusing the Vibe50 with the Synergy N9 or even the MA Stratus? I've seen two samples of those birds eating crown gears in flight which, in the end, proved to be an improper mesh but since the materials used were different (one metal and one nylon) it could happen.
Another way of seriously damaging that tail output gear would be to run a high end gyro with maximum gain on sudden stops but... once again, it would be the "fuse" that would blow up, saving the crown gears.
Bottom line, although the V3D is a bird that should be built by someone with some experience coupled with a tiny bit of OCD, the crown gears are definitely NOT a problem on this machine.
PS - Tell them to get another excuse for you not opening your eyes and see the matrix for what it really is
"Perfection and patience usually walk side by side..."