is macbeth to blame for his own downnfall?

Yes, got to give this one to Macbeth!

You need to consider that nobody made Macbeth do anything. Macbeth's tragic flaw, all protagonists in all tragedies have a tragic flaw, is his greed and ambition combined with the fact that he is kind of a coward. He stumbles his way through successive murders until he becomes King. Unfortunately by that time, he has pretty much sold his soul and become a socio-path that nobody likes.