The Dharma is descriptive, never prescriptive. It merely describes conditions, causes, and effects, and presents us with choices. Rather than reacting habitually, we can decide how to act, how to respond.
Now, saying “A Buddhist does not harm sentient beings intentionally” is descriptive, not prescriptive. It merely states that s/he has right thought (compassion) and right conduct (non-harming). It is purely descriptive indeed, because without this thought and this conduct, one is not a Buddhist.
On the other hand, to say “A Buddhist should not harm beings” is not only prescriptive, it is false, since there is no Buddhist who harms beings intentionally. It is like stating that water should be moist, or that fire should burn. If water were not moist, it would not be water. If fire did not burn, it would not be fire.
There is a fine line between self-righteous pride, which is an afflicted emotion, and fear (doubt, connivance), but we must learn to walk it, for the benefit of all. It is not only the “victims” of wrongdoing, but also the “perpetrators”, who suffer.
Cultivate radical universal compassion, without pride or fear.
Revering and trusting in the Buddha, we will wear the armor of patient endurance.
We will cherish neither our bodies nor our lives, but care only for the unexcelled Way.
Repeatedly we will be driven out and exiled from our monasteries and stupas.
Remembering the words of the Buddha, we will endure all harms.
We will go everywhere to share the Dharma entrusted to us by the Buddha.
We are the apostles of the World-Honored One.
Facing multitudes without fear, we will teach His Dharma well.
—Lotus Sutra, Ch. 13