And if you're buying a second hand phone, how do you know it's repair history?
And if you're on a plane or in a hotel, how do you know the repair history of your fellow travellers / lodgers?
The risk of bad repairs is not taken solely by the owner at the time and bad repairs involving these batteries are a threat to life.
But you are ok with cars speeding down the roads not knowing what kind of person has repaired the brakes, wheel bearings etc.? If there is no law overseeing car repairs, why should laptops and phones be different? Life is full of risks and I am very content to let Apple products loose on the street which have been repaired by non-Apple agents.