I'm just wondering what Hindus think of apostasy. Do we discourage it? think low of it? is it a crime according to Vedas?
In Sanatana Dharma or Hinduism the Vedas are the supreme authority.All the other texts, like Smritis etc, must derive their validity from Vedas only.
From wikipedia,apostasy means:
..abandonment or renunciation of a religion by a person. It can also be defined within the broader context of embracing an opinion contrary to one's previous beliefs... to mean renunciation and criticism of, or opposition to, a person's former religion,
So,to commit apostasy a Hindu will have to 1)criticize/oppose Vedas & 2) will have to embrace an opinion contrary to Vedas(his previous beliefs).
But both of those acts are condemned in the Hindu shastras.
For example speaking ill of ,criticizing the Vedas is equivalent to committing one of the 5 grave sins(mahapatkas),as seen from the verse below.
Manu Smriti 11.56. Forgetting the Veda, reviling the Vedas, giving false evidence, slaying a friend, eating forbidden food, or (swallowing substances) unfit for food, are six (offences) equal to drinking Sura.
(Note here that drinking of Sura is considered as one of the 5 major sins in Hinduism).
And, Hindu scriptures also declare that those beliefs,opinions,traditions ,that are not based on the Vedas are false and useless.
Manu Smriti 12.95. All those traditions (smriti) and those despicable systems of philosophy, which are not based on the Veda, produce no reward after death; for they are declared to be founded on Darkness.
12.96. All those (doctrines), differing from the (Veda), which spring up and (soon) perish, are worthless and false, because they are of modern date.
So,conclusion-Hindu scriptures clearly condemn apostasy as a sin as it involves 1)criticism of Vedas(former religion) and 2) belief in other traditions/faiths that are not based on Vedas .
Hindu scriptures frown on abandonment of Hinduism and adopting another creed.
Vyasa says, '..The rejection of one's own creed, the practice of other people's creed, ......- these all have been pronounced by persons conversant with duties to be acts that no one should do.’
Mahabharata Santi Parva Section XXXIV-XXXV