They argue that the amount of milk 'wasted' on such a day can feed thousands of poor instead. Why this 'excess' then ?
First of all, those who find this practice a wastage are adviced to use milk in a token way, by using a reduced and diluted form of it.
Now having said that, let's examine the beliefs and logic behind such act and how right or wrong it is to call anyone a fool for following the custom.
According to the science of Ayurveda, every person has 3 components in them:
1) Vata (Air)
2) Kafa (Cough) and
3) Pitta (Acids)
All three elements are necessary for smooth functioning of our body. However, when the proportion of these components goes out of natural balance, the body begins to suffer under various ailments.
During the month of Shravan, the Vata component of a person gets higher in proportion. During that period, a person must avoid food that increases the Vata component. For example, green leafy vegetable contain higher amounts of Vata in them. Thus a person is asked to avoid them during the rainy season (especially Shravan month) to avoid the ailments caused due to excess of Vata. During the rainy season, the cattle also eat lots of grass, and hence their milk is high in Vata and, in modern times, is succeptible to viral infections. Thus, milk is considered harmful during the Shravan month. Thus Ayurved advices us against consuming milk during Shravan.
In Sanatan Dharm, Bhagwan Shiv is known to consume the poison which came out during Samudra Manthan (Churning of the Oceans). Thus, it’s customary to offer whatever is poisonous to Bhagwan Shiv. So the Hindus offer milk over shivling (Sanskrit for symbol of Shiv) during the month of Shravan as it is considered akin to a poison by the science of Ayurved.
Hinduism says “Feed to others only what you can eat for yourself (Which means, do not offer to others what you will never consume), always give the best to others and do welfare for all. Always take care of the poor and feed them the fresh and healthy food”-(From the Vedas).
Now if we feed the milk or green leafy vegetables, which is poison during the Shravan, then it’s a sin as it will cause them diseases. Instead, we must feed fresh food to poor folks which we eat as well.
Hence, to the ignorant ones who do not know any better, let’s just clarify at once that Sanatan Dharm is a spiritual philosophy and a way of life. Science is something inherent to it and at the same time it’s a philosophy much beyond those realms.