Indulgence in animal killing for the taste of the tongue is the grossest kind of ignorance. A human being has no need to kill animals, because God has supplied so many nice things. If one indulges in meat-eating anyway, it is to be understood that he is acting in ignorance and is making his future very dark. Of all kinds of animal killing, the killing of cows is most vicious because the cow gives us all kinds of pleasure by supplying milk. Cow slaughter is an act of the grossest type of ignorance.
From Srila Prabhupada's purport to Bg 14.16