The Karma of Criticizing the Guru
Rinpoche gave this advice regarding students who had taken one lama as their guru, but then criticized and talked badly about that lama.
I was telling a student that during a great initiation the lama who is giving the initiation is [seen as the deity]. The lama says “You should listen and do what I advise. Do not belittle or give up [the guru].” This is giving a pledge, or samaya, to the lama.
[Disparaging the guru] is the most dangerous, heaviest negative karma, and it is the first root downfall. It seems people who gossip and criticize the guru, or give up the guru, do not think about this.
They have taken that lama as their guru and due to the vow given during the initiation, [criticizing the guru] is very heavy karma. So when they break that vow, there are eons of suffering, and when they pass away they are reborn in the hell realms and have to experience the heaviest suffering in the lowest hell realm. Even if they are born as a human being due to another good karma, they cannot find a perfect guru for eons.
Also, they pollute all the students that they meet and that they see. They degenerate those students’ minds and cause them to also be born in hell for a long time.