Consider another angle. Maybe Michael isn't Laurie's id. Rather, Laurie is Michael's super-ego. Michael wasn't waiting for the opportunity to kill again. He could have done that at any time. He was waiting to be judged for having killed. This is why he follows Tommy first. He can feel a connection with Tommy. Tommy is just like him, a little boy full of imagination and potential. And, Laurie looks after Tommy. Like Judith didn't look after Michael all those years ago.
This means Laurie's repression is even more important to the story than already suggested. She isn't free of Michael's violence (up to a point--and that point matters) because she doesn't have sex and do drugs
(Notably, Michael probably has no idea Laurie was smoking in Annie's car. He's following them, but that doesn't mean he can see what's going on inside.)
but because being that pure, virginal girl, she can pass judgment on him. He wants approval. He wants disapproval. Whatever he wants, he wants it from someone better than ineffectual doctors, judges, police, better than his parents, better than his older sister. So, he waits. Given the details introduced in Halloween II, we know he's waiting for his younger sister, but within this film itself, why does he come back now? How does he know he can find someone?
Or has he just gotten bored in Smith's Grove.
Perhaps his inspiration came from somewhere else. Maybe he didn't just stare at the wall. Maybe that past Saturday night he was watching Fantasy Island because some nurse had been nice enough to move him into the common room--I imagine he's in there with a catatonic Randle McMurphy even though that guy should be in a hospital many states to the west. That week's episode had a Vietnam vet (Greg Morris) seeking a reunion with his former sergeant (Christopher George) only to really want revenge. That episode also had a roller derby skater (Anne Francis) who wanted to become a refined lady to get approval from her daughter's potential in-laws. Let's say Michael watched that episode, and for an hour that Saturday night, he was drawn out of his catatonia because that is the power of television, and somewhere in his head, he twisted these two plots together. He wants to go back to Haddonfield for a reunion, for revenge, and to be accepted. (And Dr. Loomis is his Mr. Roarke, I suppose.) And, this jumbled fantasy only comes into focus when he sees Laurie Strode--and either she just reminds him of what his sister Judith should have been like or (considering Halloween II) he recognizes her more explicitly as his younger sister, though she was far younger when he last saw her. And, she's there with Tommy Doyle, a boy like he should have been. And Laurie is protective of the boy even in that brief time Michael can see them. And, he knows that this is the person he seeks... But for what? Is it a reunion with his little sister? Is it revenge, a second act of mindless violence to demonstrate his role in the world? Or is it acceptance, because she has what he doesn't--self control. But then he gets her friends out of the picture, he sets them up for her to see, like a cat offering up its latest kill at the front door, and he wants approval. He has acted on impulse, punished these immoral teens. And, all Laurie has to do is give him a nod of approval. Michael never directs his violence at Laurie until she fails to approve of his tableau. She is horrified. She cowers back into the hall and against a wall. And, Michael is there in the dark, waiting to surprise her, to thank her, to embrace her, to be embraced by her. But, her response is all wrong. And, his fantasy refocuses. Maybe it was revenge he wanted. He brings down the knife, cutting her arm, and sending her falling down the stairs...
Or maybe it was last Tuesday he was in the common room, and he watched the latest episode of Three's Company, and he saw Chrissy get taken in by that guru, and this triggers his Thorn Cult mission... Except the Thorn Cult isn't part of the Halloween story just yet.
Or maybe it was The Love Boat, and Michael saw himself in Bobby Diller (Charlie Aiken) lying to all the crew members because his parents don't pay enough attention to him. And, he thought back to when he killed Judith so his parents could pay more attention to him, and it backfired because they sent him away, and how long has it been since they visited anyway? Staring at the wall all the time really messes with your sense of time, one day blends into another, and he can't remember if his parents came to visit last week or a decade ago. And, he misses them. So, back to Haddonfield he goes. If his parents won't come visit him at Smith's Grove, he will go see them. But, he gets to the house and no one is there. No parents. No baby sister. And the rage inside takes over. He will kill every last person in Haddonfield until his parents will finally pay attention. Starting with that teenage girl he sees outside the house with that boy. But, that girl seems nice, and the boy reminds him of a time when parents paid attention, and older sisters weren't too busy having sex to play a board game with him, or at least help him sort out his trick or treating hoard. But, he follows them. If he can' thing his parents, he can have these two. So, he starts to kill everyone around them, and he leaves them like gifts for this new surrogate mother, this new surrogate self. But, she disapproves. She backs into a corner afraid. And, that just won't do. He brings down the knife, cutting her arm, and sending her falling down the stairs...
Or maybe he'd seen every episode of the short-lived Who's Watching the Kids? and he actually missed those nights when Judith would babysit him. And he felt bad about what happened all those years ago. He just wanted to go home and apologize to Mom and Dad and they could be a nice happy family again. But, alas, the house was empty when he got there. A neighborhood dog even had the audacity to wander in, like people hadn't lived there in a long time. And, if Mom and Dad could not only send him off to live in that horrid hospital, but also abandon their home, then damn it all, damn the world. The killing would continue tonight, and it would never stop. Later as he sat down to cut eyeholes in a stolen bedsheet, because if you've gotta kill, you might as well make it fun, he wondered about old friends from when he was a kid, about what masks they might be wearing on this special night. And, would they join him in his rampage or find themselves among his victims?
And, maybe, as he lay there on the lawn in pain, after that nice old man Dr. Loomis had shot him six times, Michael thought back to the common room at Smith's Grove. And, he wanted nothing more than to get back there, because Diff'rent Strokes was premiering that Friday night, and he had always dreamed of being adopted into a nice new family, maybe one that would visit more.