Well, this is how I see it:
A solid piece of wood is also made from the same stuff that tissue paper is made from, but if you' re wiping your blade with tissue paper and a small piece slides over the edge, it won't be a big deal. Now, try the same with a block of wood over your edge and....I think you know what will happen to this one!
Also, as a matter of interest, Rhino horn is made from keratin as well (same as hair and nails), but that is very hard.
It would be like slamming your shave ready blade closed on your scales if it does not centre perfectly. Edge=ruined.
The densities thickness and composition of keratin makes all the difference.