The flip-side of this is that there are so many activities that people do all the time that carry risk. Plenty of them are not really necessary, and create some risk for other people, and yet they are perfectly acceptable.

A good analogy is the use of candles. They are pointless and fundamentally dangerous, but some people like them. People who like them even think they are calming, which is a very bad reaction to an open flame from a risk-assessment point-of view.

If i knew my neighbour liked candles, i would hope that they are being safe and accept that they have a right to take socially-acceptable amounts of risk, not berate them on the internet.

I don't see how repairing battery-containing electronics is any different. Both are unnecessary, and both could turn a small mistake into a fire.

So, I'm quite happy replacing my own phone battery with reasonable precautions, but no, friend, you may not charge your sketchy e-bike in my hallway.

The level of risk that is acceptable is socially defined, and far from the black-and-white view that some people seem to have.