So who is even prevented from doing chemistry? That's easy: people who are or/and: lazy, uneducated, unmotivated, incapable of research or extremely cheap.

https://en.wikipedia.org/wiki/Means,_motive,_and_opportunity

In U.S. criminal law, means, motive, and opportunity is a common summation of the three aspects of a crime that must be established before guilt can possibly be determined in a criminal proceeding. Respectively, they refer to: the ability of the defendant to commit the crime (means), the reason the defendant committed the crime (motive), and whether the defendant had the chance to commit the crime (opportunity).

By your own admission, the process greatly reduces the number of potential perpetrators with means. By dragging out the process and requiring more labor and planning, it diminishes motive - if I can head down to the chemist's to buy some acid to splash in your face, infidel, I'm a lot more likely to do it than if I have to whip out my bunsen burner and titrate for the next 30 hours because my crime of passion has just become a crime of premeditation. Opportunity? There are far more people who smoke pot than grow pot and it's literally a weed.

Had a buddy. Was interested in GHB right about the time it was outlawed, long before it became one of two favored date-rape drugs. We had a conversation at the time - the precursors were readily available, but the price on enough precursor to make 5ml of GHB was every bit as high as the price on enough precursor to make 5L of GHB because if you intended to make 5L of GHB outside of a commercial chemical enterprise, you were guilty of trafficking not possession.

So my buddy said fukkit and made a fuckin' gallon and a half of GHB.

He hadn't gone through a soda can's worth before he decided he wanted nothing more to do with GHB. I guess he made himself sleep for three days by accident once. That amount of controlled substance was an attractive nuisance; you can't show it to anybody, you can't sell it, you can't raise the attention of any local narcs because you're looking at Big Time if you get busted. So he poured about 80% of it down the drain and moved on to other things.

It's a pain in the ass to buy cold medicine in the United States. You can still get it, but you can get it about one cold at a time. This is because the active ingredient pseudoephedrine is a vital precursor to crystal methamphetamine... but you need more than one cold's worth. the underworld adapted but now you aren't talking about one couple cooking in the rental apartment, you're talking about a criminal enterprise which you can prosecute appropriately.

As a thought experiment, let's pretend you're a jihadi hell-bent on annihilation of your fellow Polish citizens. You're clever, you're intent, you're patient. Your goal is not to advance your own knowledge, your goal is to devise maximum bloodletting. As such, you will likely find the recipe and procurement process that maximizes pain and minimizes effort. While you are doing this, you are buying chemicals, going to stores, becoming known, etc. Pretty soon you're the mad bomber and it's far more than local police watching you; you're now a target for Interpol and there are surveillance vans outside your mom's house.

If, on the other hand, you're an innocent experimenter (as you are), your purchases and behavior very much do not match those of jihadi terrorists. You likely aren't purchasing exclusively precursors that lead to terror weapons. Sure, you've got some high molarity acid but there's a lot that can't be done without high molarity acid and they know where you live, they know where you go to church, they know who you talk to and they know that should you decide to shift towards terrorism they'll probably know before you do. The entire pattern of your behavior will change.

A qassam rocket is literally pipe, sugar, fertilizer, TNT, a cartridge and some BBs. The chemistry is pretty well settled, far less sophisticated than what you're doing and the materials are much more readily available. Mossad got the guy who came up with them anyway. Meanwhile, nearly all IEDs have a particular Timex watch at their hearts. Sure, there's a million different ways to do it but that one Timex is easy to get, easy to mod, and doesn't require any improvisation.