Actions based solely on tradition and unreasoned belief, even when done in good faith, generally cause more harm than good. The festival of Nag Panchami celebrated by Hindus sometime around July-August brings this issue to the fore. During this festival the bhakt jan worship snakes by offering them sweets, flowers, and milk. But if these were just offerings, things would not have been so bad for the snakes. As it happens, the snakes are also fed milk.
Milk is a product which is exclusively produced by mammals to feed their young ones. Members of the animal kingdom other than mammals including reptiles, birds, amphibians etc. do not produce milk and thus are very unlikely to have a liking for it. Not just non-mammals, a significant proportion of adult humans lack enzymes to properly digest milk, which is meant for the consumption by their young ones, and are lactose intolerant. Snakes are no exception. They do not possess the necessary enzymes to digest milk. In fact milk is toxic to snakes and generally proves lethal if consumed. But if snakes do not drink milk, what about those who claim to have seen them doing so on nag Panchami. As it happens, a snake is kept thirsty by the snake charmer for many days prior to Nag Panchami. The snake is dehydrated to such an extent that it will consume any liquid that is brought in its proximity.
Not just forcefully feeding milk to the snake, the entire ritual including coercing them to move around; sprinkling turmeric, flowers and vermillion; and carrying them around hordes of people is mentally traumatizing to the poor animal. The stress it go through turns out to be fatal most of the times.
The association of nags with Lord Shiva has elevated their status to the divine. We wish to get rid of evils from our lives by serving them. However, our ignorance and blind faith have clouded our thinking so much that we find it difficult to accept even the most basic facts. If we treat snakes as humble living thinks, like many other marvels of the nature, and just let them be, we would be doing them better service.