None of this can really be pinned on the use of passive voice. Attention is naturally drawn by the beginning of a sentence and to the end of it, and while the passive is a powerful tool for reordering sentences, its function is equally well served by verbs with the opposite alignment. There is nothing about "there were mistakes" or "mistakes happened" that attributes more agency to anyone than "mistakes were made", but only the last one is passive.

Rather, there is a rich history in English prescriptivism of misdiagnosing and blaming the passive for all ills.

http://www.lel.ed.ac.uk/~gpullum/passive_loathing.pdf