If it's such a bad idea, why do they have very explicit instructions on how to do it in the manual? I have been that good Samaritan probably half a dozen times using my 2016 F-150 to boost stranded motorists, so not the most techy truck by today's standards. I do it according to those above manual instructions but was told by a mechanic a long time ago to make sure everything electrical in the boosting truck was OFF, except for the heater fan on low, engine idling.
I too have been carrying booster packs in our vehicles but also have booster cables. Guess it's time to ditch the booster cables and just keep the newer booster packs in my roadside kit.