By a webcomic and common sense. If you look at the society's work, you'll see plenty of people growing beard out of sheer will. People, fruits, appliances, lizards, everyone that wanted a beard got one. Dr McNinja's research only confirm what should be common sense.
Now as for the superiority of beard over non-beard, it too should be self-evident. However, it can also be proven in a great many way.
First is the ontological proof, of proof by being. That which exist in reality is greater than that which does not. As such, a beard is greater than a non-bear.
Then is the inductive argument. It is acknowledged that the greater being in these parts is Toady One. Let us look at Him.
Yes, that's a beard. Furthermore, when He created his most perfect creation, dwarves, which of His attribute did he sees fit to grant them? His cold, wet skin? His superior mathematical abilities? His insatiable thirst for soda? None of the above, but His beard. How then avoid the conclusion that the beard is a Great Thing?
One could go on, but I'm afraid that if you are not convinced by this point, no display of Sense or Reason shall convince you. The only way I could see would be to have you experience first hand the glorious feeling and superior intellect and wisdom that results from being bearded. As such, I've taken the freedom to prepare a Brain Growing Operation for you, if you'll just proceed and grow that beard you won't fail to be convinced.