Lets just assume hypothetically someone with strong dream control has mastered shared dreaming to the point they can infiltrate anyones dreams and exert control over the dreams of others.

Would it be wrong to cause people to have nightmares? Would the intention matter? For example, causing a nightmare while driving a secret email address into the target with instructions to send an email immediately after waking for better recall vs a regular dream message, or doing it simply to spark lucidity in order to guide them into an awesome lucid dream, vs doing it just to mess with people, or for revenge scenarios like maybe you are in jail so you torture the judges mind in order to attemp force giving the lightest possible sentence in exchange for making the nightmares stop. All hypothetical stuff here.