There's no need to fight over it because you have the choice of which way to do it. One way puts a risk to the battery (inserting the charge connector with the charger switched off), the other way is a risk to the charger.
The problem is the inrush to the charger's output capacitors. If the charger isn't switched on, a very high current will flow from the battery to the capacitors, which is why you get a spark at the connector. The spark will eventually damage the connector. As I said before, the jack sockets on bottle batteries are easily damaged. The 3-pin XLR plugs and kettle plugs would be more robust against that. The second problem is that that high current also goes through the charge mosfet and fuse. There's a small chance of blowing either, though the chance of the mosfet going is so small that you don't really have to worry about it.
If you switch on the charger first, the inrush comes from the charger itself. I don't fully understand all the circuitry on the output side, but I would guess that the inrush is damped enough to not do any damage. Maybe some chargers are or used to be a bit suspect in that area, which is what caused people to decide to plug the battery in first5. A lot of these strange rules and ideas go back a long way before the systems were properly developed. Maybe to the days with SLAs without BMSs.
Whatever the reason, A charger is a lot cheaper to replace than a battery. I guess a lot of people will be writing off their bottle batteries, when they plug in the switched off charger, but there we are.