It seems silly to me. I work in the transport industry, and our main clients are 2 aluminium smelters. They blast huge holes in the ground, and use giant earth moving machines to remove the raw materials. It's heated in giant crucibles to a molten form, then anodes are dropped in and massive amount of voltage are applied to purify the metal. The ingots, logs, and slabs are then loaded by forklifts onto trucks, and are brought to our yard. We load it into containers, and rail it by electric train to the wharf, where more heavy equipment loads it onto boats that will deliver it around the world. I can't name our customers, but I can assure you that the bike you're riding has at least one or more component on it that came from the ground here. And bikes still have rubber tyres. Sure, it's not as wasteful as a car, but the environmental impact is there.

Food for thought.