Do the witches in macbeth play a central or collateral role in shifting the ambitions and actions of the plays characters

Macbeth's demise was due to fate - I would choose character and say that  every point that Macbeth had choose to do something terribble so then had , he received some kind of sign telling him to go back but of course he dosent listen to  it. The witches had pumoed  him up and told  him that he would have been  destined to rule over Scotland.  they play a collateral role you cant blame them for macbeths since, but they still sorta kind did help him push down the path of terriblenes 

D. prior knowledge