I think the only limit should be if they are willing to do the work to learn. "Secret" knowledge is good for tricking people into thinking you've got something special without needing to prove it to them.
I'm not offering secrets. You will need to learn things sequentially building one on the other. It is all there but you might not get it without the prerequisite. No different than needing addition and subtraction to do algebra.
Yes people use the allure of the forbidden to ensnare others. I’m not talking about calling something forbidden for that purpose. I’m talking about not teaching a lunatic how to build a bomb simply because you know how and they have money. Some things have been hidden because the average person would miss-use them. There is a rule in one such discipline that for every step forward in gaining this knowledge you need to take three steps towards moral perfection.
How to build bombs with common unsuspicious parts is already widely publicly available information. The truth is that the dedication to learning builds character. Most people are far less evil than you think or too stupid and lazy to do 1 internet search. Either way, same effect of safety.
Take martial arts for example. The knowledge is there for anyone to find out which ones work and just go practice. The world around us shows that the people picking bar fights couldn't be bothered. The people who could be bothered don't go around picking fights.
