Krishna now addresses a specific danger: people who invent their own harsh austerities, ignoring what scripture actually prescribes. These people are full of hypocrisy and arrogance. Their goal is not inner purification — it is showing off, or satisfying their own desires.
Driven by desire, attachment, and brute force, they put themselves through extreme practices. Imagine someone who fasts not to purify the mind, but so others will call them a great ascetic. That is dambha — pretense wearing the mask of discipline.
Krishna makes it clear that severity alone does not make an austerity worthy. What matters is the intention behind it. This shloka pairs with the next one (17.6) to form a complete warning.