The Gateway Theory is correct, incorrect, and deeply flawed.
It's a matter of perception, and I hope you'll keep an open mind.
The Gateway Theory about drugs is that if you try marijuana you will try other drugs. This is true in the aspect that if you try marijuana, and actually enjoy it, you may be curious about other drugs. YOu may think, "this is great. What else is the government lying to me about?" It's also true in the aspect that because it's illegal, you're weed man might introduce you to mushrooms. Maybe mdma, if you're lucky, but very few dealers deal all drugs. I've noticed a naturalist vs. chemicalist separate in dealers and most are naturalists.
I tried marijuana and it made me curious about other drugs. I believed that because I had a pleasant experience on marijuana, I'd have a pleasant experience on other Schedule 1 Controlled Substance drugs. The fact that they're scheduled in the same category is misleading.
Mainly, because marijuana was categorized as a Schedule 1 Controlled Substance, I believed other Schedule 1 Controlled Substances could be as pleasant, harmless, and as fun and interesting as marijuana. I was mistaken.