Taking that class is like a warning, but one given to subliminally say, "this is weird, but it's good weird. It's the right way, it's positive, and when it happens to you, it's a good thing."
Imagine if I sold cheap shampoo that used chemicals so harsh, they would burn your scalp and perhaps damage your hair. If I just sold it to you, you'd come back and say, "what kind of garbage are you selling me? It burned my head!"
But if I said while selling it "now, this shampoo has some active ingredients that are going to give a bit of a tingle. This is how you know it's working! The tingle invigorates the scalp and will make your hair more lush and beautiful!" you would look for the "tingle" i.e. burn, and consider it good. You would now falsely believe in my crappy product, and maybe sell your friends on it. Months or years later, you might all be bald and in pain, but by then it's too late.
The only difference is many people would probably be less trusting of the shampoo lie, than they would be about Scientology's course.
P.S. I am not, in real life, a shampoo salesman.