What is gained by selling rattlesnakes to children in stores? The harms outweigh the benefits. People who need to study rattlesnakes have ample opportunity. Similarly, chemicals that are extremely risky to handle should not be sold to children but introduced in a classroom. (OP's example is different because the chemistry sets he complains about not being available actually are available to children today.) It's not like there isn't plenty of other chemistry to learn about, and this setup makes it more likely that more children will survive as chemists to make important discoveries. (See the David Hahn story.)