Devotion to Guru in Mahayana seems extreme and what Lama Yeshe said about puts me off a littile

From the article on Lama Yeshe Wisdom Archive:

The karma from forsaking one’s guru is worse than the karma generated by Hitler and Mao Tse Tung. Mao Tse Tung caused harm to many holy beings, but they were not his gurus. In the world, someone who kills many millions of people can still achieve enlightenment in that same lifetime. But generating heresy toward the virtuous friend and giving up one’s devotion to the virtuous friend makes it difficult to achieve enlightenment, even if one practices tantra with much hardship. It will be like taking a rebirth in hell.

It seems very extreme and I see no empathy in such devotion. How I should view it? Am I missing some context?