Be respectful, kind, beneficial and affectionate to all Dharma friends. Never harbor bad intentions, anger or deceit towards them, nor inflict harm upon them. Regard Dharma friends as your vajra brothers and sisters. Do not slander them. Do not gossip divisively about either your Dharma friends or other practitioners and teachers. Do not harm your own practice by indulging in impure perception. Extend pure perception as much as you can. A genuine yogi or yogini has unrestricted pure perception. Do not restrict your pure perception to your own root-guru alone. Acknowledge the timeless enlightened quality in each and every being.
Vajrayana in general is training in pure perception—Dzogchen is even much more so. How can you call yourself a practitioner of Dzogchen if you spend your time defaming, finding fault with or criticizing others? Maintain the view of pure sight, sound and awareness. This is how samsara and nirvana actually are, pervaded by the three kayas or three vajras. Sentient beings might not be aware of their Buddha Nature, but they are nevertheless endowed with the three kayas. You need to train in pure perception by accepting and respecting the three kayas in everyone. Great masters do perceive all sights, sound and cognitive activity as infinite purity. Once recognition of awareness is stabilized, there is no more impurity to be perceived. Train in this by thinking: "As the Buddha Nature pervades all beings, not a single being is unsuitable." The more you respect Buddha Nature in others and train in pure perception, the more your own practice will progress.
Slandering beings is slandering buddha nature; stop doing that. If due to your own impurity you perceive mistakes in other beings, at least do not voice them. If your awareness practice is too weak to sustain pure perception naturally, try to develop a rapport within an intellectual understanding of Buddha Nature in others. Know that your impure perception of others only happens either because you have not recognized genuine awareness, or because that recognition is not developed. Criticizing and slandering others puts you out of tune with the enlightened essence.
You mainly harm yourself. The most unrealized so-called practitioner of Dzogchen can at least keep his or her mouth shut, even if he can not actually maintain the view.
A deceitful person sees everybody with suspicion and finds many mistakes in others. A pure person naturally perceives others to be good. How much more so does a perfect yogin or yogini. He or she has the perception of infinite purity. They will actually perceive all forms as the bodies of the deities, all sounds as mantra, and all thoughts and emotions as the display of awareness. In their perception of pure sight, sound and awareness there is no attachment to friends, or aversion to enemies. Awareness itself being free from concepts of good and bad, proper and improper, they perceive everything as great equanimity. They do not accept or reject friends or foes. They perceive not the tiniest speck of impurity. As is said, "Arriving at a golden island, one cannot find ordinary earth or stones even if one searches for them." In general, good and bad are your own perception, so you cannot possibly see faults in others when your own are purified.
--from a teaching by Tulku Urgyen Rinpoche