...And for the most part, it is considered an honour to be chosen as a sparkling's human mentor.

There are however parts of human society who are still prejudiced against Cybertronians, and issues of being careful not to pick someone who secretly may be of such a mindset. There have been cases where a bad pairing has been made and the sparkling has suffered abuse from their human mentor. The consequences of that can vary from them merely being shy of humans to being rabidly anti-human.