Tradition has been an excuse for many wrong things - the caste system for example.

We do not know why we do not eat meat! Some will say that cows are holy! But I do not buy that argument simply because I don't see anything special in cows compared to other animals. The only possible reason is that they give milk! In modern times, we hardly drink milk from cows anyway. Nevertheless, cow milk is precious in villages around Nepal. And they would rather get milk everyday for years from the cow than have meat for a week. I can see why they would consider it sacrilegious to consume a cow when it is worth so much more. I guess we have to look at everything in context. In the US, milk and beef are both aplenty, so if you like beef, I don't see why you shouldn't have it.