How Buddhists Can Destroy Buddhism

If a [practising] Bodhisattva acts in such a manner [which harms other Buddhists for personal advantage], he is no different from a worm in a lion’s body, eating away at the lion’s flesh. This is not something a worm living outside the lion can do. Likewise, only disciples of the Buddhas can bring down the Dharma – no externalist or demon can do so.
– Brahma Net Sutra

The lion is the fiercest of animals, and when he roars all the other beasts flee.
In the same way, people who have taken the precepts are likened to a lion;
no other beings will bother them.
However, just as worms that live in the lion’s body dare to feed on the lion’s flesh,
so too, disciples within Buddhism can undermine the entire system.
Buddhist disciples themselves are capable of destroying the Dharma,
more so than the people outside Buddhism.

– Master Yen-p’ei