What kind of harm? Do you actually know of someone who was harmed in that way?
There's two types of harm. First, as explained to me, if you hear pointing out instructions too soon they become a cliche. Instead of having the effect they would have had if you heard them when you were ready to understand them, they just become a phrase to toss around, not much different than a fortune cookie. The second is the danger that they might be misunderstood. And if your pride prevents you from admitting that you have misunderstood them, you've effectively vaccinated yourself against the truth. This problem is not limited to dzogchen, you also see it in Zen, Theravada, and probably outside Buddhism.
Obviously if you teach the truth widely, there's both the chance that it can be understood or misunderstood. If ChNNR does so, that's his choice. Other teachers advise differently, but that's a metter of judgement, not of right or wrong.