Upload & Sell: On
As Nathan Hobbs explained, the front protective element is over the main fluorite glass element, which is indeed very soft and easily damaged. Fluorite is so soft that normal cleaning methods can easily scratch it. So some protective element is required. Canon made it serve as protection, and gave it good coating. The part that it has that no filter around provides is the curved surface, in order to minimize the internal reflections that can occur off of a flat surface filter. I guess Canon could have considered making it a user replaceable item, but I think they wanted to keep things clean inside, plus maintain a waterproof seal. Plus if it was removable, some users would leave it off, and damage the main element, which likely would cost well over $1000.