I dare say most chargers out of the box won't do even 10A, let alone 20A (even my trusty iCharger 406 Duo can only do 10A without external discharge bank - or maybe when used from a car battery, but I've never used it without a PSU). But is that really a good reason to outright ban anything outright? Maybe in a racing series, but on tracks, even for open practice? Doesn't convince me. Someone had an unnecessary idea and the horde blindly followed - at least that's my theory. You yourself have seen the myths spread by people who don't really understand electronics...