I drop my 24 L from about 1 foot high with no issues. Typically i take very good care of my lenses. The fact of the L lenses are not all metal would not discourage me from buying them. Just treat them as jewel!
1DX, 24mm f1.4L II, 50mm f1.2L, 85mm f1.2L II, 135mm f2L, 24-70mm f2.8L II, 70-200mm f2.8L IS II : D800, D4, 24 1.4G, 35 1.4G, 50 1.4G, 85 1.4G, 24-70 2.8, 70-200 2.8 VR II