Deliberately ‘poisoning’ someone is always ‘evil’.
But, there are no such things as ‘poisons’. Every substance can be toxic to the human body when ingested. When the toxicity of this substance becomes harmful to a person, it becomes a poison. Salt or vitamin C for example, can be poisons resulting in death when ingested in large quantities, but we don’t consider them poisonous substance. Same with arsenic, except that the dosage of lethal toxicity of arsenic is much lower.
In that sense, poison is like Evil: it’s unredeemable and not very useful in conversations. Toxicity, like wrongness, is more scalable and therefore more useful IMO.
IMO, it’s not very useful to talk about Mind Control in terms of evil or not. Taking control of someone’s mind and make them do things that go against their very believes and do harm to themselves or their loved ones is all the way up in terms of wrong. Using hypnosis to help a consentant patient to help them stop smoking is not even on the scale of wrongness, even if both can be considered mind control.