As they say, stereotypes are always based in some part of reality. The stereotypes regarding Crack Cocaine are generally an accurate portrayal of what happens when Crack Cocaine is used. Like every addictive substance, the pharmacology of the drug is part of the story, while the onset/peak/duration (pharmacokinetics) also play a huge role in how people are affected. There is a reason people can, say, go to the bar, socialize or what have you while using insufflated Cocaine. It's also the reason why Crack Cocaine is not used in this way.
I've met people who claim they can use Crack Cocaine with essentially complete control. I'm sure they exist. I'm not discounting anyone's experience here. These folks exist just like the 3g/day intravenous Heroin addict who makes six figures, is emotionally available to their partner and is never late to his kid's little league games; that's to say they're pretty fucking elusive.
The short duration, rapid peak and intense euphoria that comes from smoking Crack Cocaine really puts it in a league of its own in certain respects. I'm personally amazed by the amount of Cocaine people can consume without their heart exploding.
A typical Crack Cocaine story I like to tell normies who are curious about it:
I knew this guy maybe a decade ago who was nothing more than a fellow junkie in my city. He got some kind of personal injury settlement. It was for something like $20,000 and naturally, it came as a lump sum. This guy was talking about it for weeks in advance. He was gonna get a car, get the money together for a nice apartment, buy his Mom something nice for all the bullshit he put her through and yes, he intended to buy a perfectly reasonable amount of drugs once the essentials were taken care of.
The day came and this dude owed me money, as he did many others to whom he had promised all kinds of shit in order to get credit. Well he wasn't picking up his phone, which pissed me off, though I knew he would at the very least have my $50 by the time I ran into him.
The weekend came and went. By Tuesday morning, the dude's phone was completely off. Our mutual dealer was a Dominican guy, the type that could be either wicked chill and friendly or terrifying depending upon how you handled your business with him. Sure enough, he was in fact looking for this guy, as he left the traphouse to "go to the ATM" with $1,000 or so still owed to the dealer for Crack.
Turns out he spent all ~20,000 in a period of 3-4 days, only taking breaks to go to the atm to get more cash. The dealer didn't think much of it, considering the dude had already spent a mint. You see, Paco was the type of guy who you paid on time. If you didn't have the money, you went in person to tell him and work something out. If you did this, he could be very understanding. If you didn't pay then actively ducked him... that's different. If you did this and he found out you spent money somewhere else, there was no way around it, you were gonna get hurt.
He eventually located his prodigal client. He shot him in the thigh and somehow smashed one of his hands, I assume with a hammer.
I've gone on way too long here already. I tell this story, as your thread was asking why people are "changed" by Crack Cocaine. Well it is addictive enough for someone to spend 20,000 over the course of a long weekend, then to risk his life to get more. It completely consumes people.
A small side note: 90% of my drug use has been Opioids/Alcohol. This is what I know and understand with the most depth. I have done all of the drugs out there though. I've used Crack Cocaine probably a dozen times. It was often my Heroin dealer giving me a free hit or people I knew doing the same. I never truly "liked" Cocaine. I didn't crave it, have dreams about it or anything in the way I did with Opioids.
Still, even as I sit here saying I don't even like Cocaine, I can testify that after taking that first hit, I would instantly start fiending for more, thinking about how much money I had, how much I could spend etc. This jones would go on for an hour or two after that hit. In that moment, if I had $20,000 as much as I hate to say it, I could probably do the exact same thing.
Of course all addicts face desperation, degradation and sacrifice to get their drugs. With Crack Cocaine, I've seen people literally acting like infants, crying, begging, pleading for another hit. If you have a particularly ruthless dealer, they might fuck with you and degrade you simply for their entertainment. I'm sorry to say I've seen that too.