Oh the horror! Someone doing something with a higher risk level than you are comfortable with.
While the risk/reward payoff on this particular escapade doesn't seem particularly good, it doesn't seem likely to end life as we know it, burn down cities, or even to kill significant numbers of people.
In this internet age you can find alarmists wanting to eliminate all of the terrible things from our society. People will take a bit of information, such as knowledge that men don't have a robust mechanism for eliminating excess Iron in the body and turn it into a campaign to eliminate Iron. This has resulted in widespread movements to ban useful stuff from our world. The nasty metals like Arsenic, Bismuth, Lead, Mercury, Strontium, Copper and Aluminum. Or those horrible toxins - chemicals - which must be eliminated from all of our food and clothing.
Once you have accurately pointed out the risks of a particular behavior, and evaluated whether this behavior will have a direct effect on you or those you know, it is time to move on. It isn't the job of any of us to tell the whole world how to live their lives.
In this particular example, some number of people will be motivated to try "fixing" their batteries. The vast majority will not cause any proximate harm. A few will breath a small quantity of something not good for them, which in some cases will result in a shortening of potential lifespan. (Remember that people who do things like this are also likely to try a large number of other potentially life shortening activities). The vast majority will find that the batteries are not restored to like new condition, and in many cases not even to usable condition. They will seldom, or never repeat the experiment. This will remain a fringe activity that has little impact on the health and safety of the world.