To kill a sacred cow

I read somewhere "sacred cows make the best Hamburgers". I dont want to go into the go into the debate of justification of eating of non-vegetarian food. But, there is some saying in Hinduism, which has been widely misunderstood and I will try to give my interpretation of it.

The saying is: "Cows are sacred and we should protect them". Its most popularly understood interpretation is that, Cow, the animal is sacred and it should not be harmed. To a free thinker, this would sound completely absurd since, off all the living animals, how come cows are sacred, why are they better than any other animal. This was the reason I never beleived in this saying and till I was a non-vegetarian, never hasitated in eating beef.

But, there is another perspective to this saying which is more implicit. It means that Cow resembles a class of creatures, which are not only harmless to you, but most of the times they are useful. We do get milk from Cows, so they have atleast one utility. Killing anyone without any reason is a sin, but if you kill someone from the category of "Cow", the gravity of sin increases manifold. Because, it is like this use the creature till you can and then slaughter it so that we can completely suck up to advantages we can gain. I got this meaning after reading "To kill a mocking bird", which also underlines the same principal. They give this idea with reference to an african american, and I am just trying to generalize it.