50-100 gallons of water compared to 500 gallons for the same amount in rice

I'm not aware of the arguments against, but the cows aren't the only thing that needs water: its their food too. Most crops that are grown on Amazon's deforested areas is to feed cows, or something to that effect.

I visited the Cowspiracy site to find out exactly what the claim was, but it's got so much research I had to ctrl + F 'Amazon' : "Animal agriculture is responsible for up to 91% of Amazon destruction."

Again, I'm not familiar with the counter-arguments, but it's interesting stuff.