Sivananda taught according to Piscean psychology (from the previous era), which required secrecy, warnings, veils.
Samael taught according to Aquarian psychology (the current era), which is open, direct, and revolutionary.
In case you did not know, you can harm yourself simply opening a door or putting on your shoes. We are infinitely capable of being stupid. So yes, someone who is foolish can hurt themselves if they are not paying attention and abiding by the instructions. For instance, the instructions are to practice once a day. However, there are people who ignore that, and practice multiple times per day. This harms them. It is not transmutation or alchemy that is harming them, it is their lust and abuse of their sexual glands that harms them.
Transmutation is not a blind, mechanical process. It is only possible because our inner Divine Mother guides it. She does not harm her children. There is nothing to fear about restoring our sexual life to the natural form we had before we left Eden, so long as we follow the guidance of the teachings.
"Do not worry; cultivate the habit of being happy." - Samael Aun Weor