Evil is cool. It can be a lot of fun to keep people on their toes - or even freak them out a bit. And it's okay even. If there's a lesson to be learned and they'll look back on it as good fun, then go ahead and try on the "evil hypnotist" costume. It's just that doing the evil hypnotist thing for real is almost always a bad idea.
I'm not going to waste time moralizing that "you shouldn't be evil because it's morally wrong", because that's completely unpersuasive. Either you agree or you don't care. Well, mostly. I could try to use dark arts to moralize you, but light arts tend to work better. That's kinda the point of this post.
So lets make a bad assumption for a second and assume that you're a completely and genuinely selfish person. Of course you aren't, but let's pretend you are. Pretend you actually care zero about other people. You've found hypnosis, and are like "Ooh! Mind control! Now I can control people to get what I want!". How should you use it to best achieve your goals? There's kinda a lot of ways to do it.
The Oxford Handbook of Hypnosis has a chapter about "hypnosis in crime". Contrary to what these "experts" will tell you, hypnosis can definitely be used to get you to do things you wouldn't want to do. Like, really bad things (Hell, people do things they wouldn't want to do when not hypnotized - as if hypnosis makes you less susceptible to that). They describe a court case where a woman accused a man of using hypnosis to get her to give him oral sex. His defense is basically "nah, hypnosis can't do that. Even ask the experts >;-)". Okay, he was probably smart enough not to smile an evil smile, but still...
The actual expert witness they called in backed him up on that. And not just "that's what our theory/lab experiments say" - it gets better. The specific defense was that "the defendant [...] suggested that she was on a beach licking an ice lolly. However, the complainant's actions were consistent with reality and not with the fantasized scenario". Wait, WHAT?!? B-b-but... What about the invisible chair real/simulator experiment? You know, the experiment where hypnotized people walk around the "invisible" chair and then rationalize a reason for their funny trajectory. Surely you must be aware of that experiment... Oh wait, you reference it in the next paragraph... as evidence that it was consensual... <facepalm>
The thing is, that's exactly what you'd expect if the suggestion works right. She "seemed aware at some level", so it's okay that she was predictably not coherently supporting her actions and probably traumatized by it - it's outright rape by deception. Oh well, at least your theory hasn't been proven wrong, and you're not a professor of the dark arts...
So yeah, it's possible. But think about it from the evil hypnotist's perspective. Even if he managed to dodge jail time, he certainly couldn't have predicted it with enough certainty for it to be worth a BJ or a few. His reputation is still probably ruined. If you look at the expected cost/benefit, it just doesn't pay out - even from a perfectly selfish point of view.
And wait a minute, this guy can literally convince a girl that his penis is a popsicle.... but he can't convince her that she wants to have sex with him? Did that like... not occur to him or something? What's wrong with this picture? The PUA crowd has never suggested "maybe if I convince her it's a popsicle...". It's just not on the radar, and for good reason.
This suggests a clearly better approach. Use your mind control to make them want what you want them to want. Now you've graduated from "rapist" to "manipulative asshole" - or if money is your goal, you have customers with buyer's remorse instead of being outright stolen from. That's a pretty big jump. You're in a whole lot less risk, since for better or worse, it's hard to put someone in jail for just being a jerk. As an upside that you hypothetically don't care about, your victims are less traumatized by their experience with you.
But there's still reputational costs of being manipulative. So maybe you can use your mind skills to be really good at giving people what they want in a way that they reflectively endorse those wants. Then you have positive reputational effects, can't be jailed, etc. The more evil approaches tend to be less stable, as I've mentioned, and in general it's really hard to track your deceptions. Shit can get kinda complicated if you're trying to design a legit parasitic mind virus. It's often so much easier to just find a third option - some value producing trade that they don't see - and bring it to the table and persuade them to take it. Once you got that, you're done. There is no "getting caught" or having changes "undone".
So even for selfish reasons it's generally a good idea to be a good guy.
Evil approaches are simpler, in a sense - and somewhat more tolerant of poor "inner game". The fact that the evil approaches require less breadth of understanding is almost certainly why it's as widespread as it is (both in and outside of hypnosis). It's a terrible reason, and not just because you get thrown in jail sooner or later - that's just the first half of the story.
The other half of the story is that "truly evil" people - in the sense that the evil is reflectively stable - are at least somewhat rare. I don't think they even exist. So far, every time I see people doing bad things - at least of the variety you get shamed for (not like telling white lies or "doing 5 over the speed limit") - it's because of some false belief or flaw that their reflectively coherent terminal values would love to get rid of - if you approach it right. Even Jeffrey Dahmer, one of the most disturbingly evil people around, wasn't terminally evil. If he wasn't so extremely needy/desperate, he'd have no motive to kill people.
Time to drop our earlier bad assumption.
If you find yourself with mind control powers and tempted to do something evil, you can probably get more of what you want by working on yourself and being good. Often this is true even if you're not talking about being evil. It's gotten to the point where when someone asks me "How do I get person X to do Y?", my first response is to work on the person that asked me, and then just watch it work out naturally. When I get frustrated with people for being stupid idiots, I've found that the most effective thing is to work on me. Why do I care that they're being a stupid idiot? Why are they being a stupid idiot? Oh... right, because of the obvious answer. Once it's cleared of emotion, it's all pretty clear. And then I'm not only remarkably more effective, but I'm in a better place myself - and these are cases where the other person is being a stupid idiot! Even evaluated from an emotionally neutral position afterwards.
In fact, we can take it further. I recently had a case where an email list interaction didn't go well even though I didn't feel like I was coming from a bad place - and I'm getting pretty good at noticing that kind of thing. And I still turned to look at myself first before trying to draft the next email. I only found a sliver in myself to improve on, but focusing on that did get the interaction back on track, and he even admitted that it was largely him. (And this is a case where it was verified by several others that I had done nothing wrong and that I was already the good guy in that interaction.)
Consider what I gained and what I lost by working on myself - from genuinely taking responsibility for anything I may have done wrong, and genuinely not giving a shit if he continues to respond poorly - instead of doing nothing. I had to give up on feeling smugly superior. I had to confront the scary thought that maybe I was doing something wrong (I made sure to check this on my own and write the response before I got outside verification). But I gained effectiveness. I became actually better than the alternative - both in emotional health and effective communication - and of course also gained the benefits of the effective communication. Pretty clear choice when you think about it. Feelings are information, not terminal values. As long as you remember to acknowledge the scary bad feelings so they'll stop trying to weigh in on your decision, it's pretty easy.
So yeah, you aren't actually evil - and there are far less reasons to use dark arts if you're not actually dark. If you're ever like "The power! the absolute power! The universe is mine to command! TO CONTROL!!" or even the far more subtle "how do I make..." or even "how do I convince..." then like, you should work on yourself - not in a moralizing and shaming way, just in a "it'll help you get what you want" way. Of course, you can still put on the "evil hypnotist" costume every once in a while to have some fun with it >;)