“How can you say that I should not repair or upgrade my phone / laptop without Apple blessing because my device could harm you WHILE at the same time I can repair my car at a third party mechanic and fucking cars have more potential to cause damage then electronics and tractors”

Easy:

The work of third party mechanics is not remotely comparable to diy repairs. They are:

1. Are strictly licensed

2. Are strictly regulated

3. Are liable for safety problems they cause.

4. Are required to carry insurance because of #3.