Hey, wait a second! Your legs are not so green, buddy.
They are fueled by chemicals obtained from organic byproducts using a process with more or less a 20% effectivity.
If your source of organic fuel is a vegetable, your legs are, in fact, green-consuming machines.
If your source of fuel is animal meat, they have to had built their own organic mass using a C fixing process that's even less effective.
Not to mention the organic fuel they have wasted themselves until you ate them.
If your animal meat came from a carnivore, it make thinks worse, as it repeats the inefficiency cycle one step more.
At some point in this chain, the organic mass should come from an herbivore -> green consumer.
So, both ways, either you destroy green things or you destroy even more green things via inefficiency.
Obviously I'm just joking, but what if you were one of those ecologists and you just read this?
No brainer: Walk with hands. Chop as many legs as you can.