I'd like to know some points of view on this topic. Was Macbeth the only one to blame for all that went wrong or should responsibility be shared with other characters too? Examples and quotes on this would be great also!
I think Macbeth is partly to blame as it was his strong sense of ambition which drove his actions forward. However it was as a result of other characters such as Lady Macbeth and the Witches who 'lit the fire' of his ambition.
No, Macbeth alone was not to blame. His wife spurred him along. He did not want to kill Duncan. However, once he did kill Duncan he became a bit bloodthirsty and started killing everyone in sight. So while Macbeth definitely is responsible for his actions, he is not solely responsible.
The author of Le Petit Prince, Antoine de Saint-Exupery, wrote, "Etre homme, etre reponsable." That is, each man is responsible for his own existence (Literally, "to be man is to be responsible.") While the ultimate responsibility for the deeds he has committed lies with Macbeth, he certainly was tempted by the evil sisters with their predictions that he would be king--"If chance will have me King, why, chance may crown me,/Without my stir"--and persuaded by his wife, who has challenged his manhood.
Lady Macbeth must certainly take a great share of the blame. She was really the catalyst behind Macbeth's actions. If she had not goaded him into it by questioning his manhood and telling him what to do and how to act (she even told him how to look in front of other people) I truly doubt that he would have done it.
Even though the witches are are an apparently evil group, I don't hold them responsible. They put the possible future in front of Macbeth, but they couldn't make him or his wife actually do anything.
It's worth noting that Macbeth was about to cancel his plans to kill Duncan when his wife challenged his manhood and his honor, pressuring him to go through with the crime. Additionally, Hecate makes it clear that she and the other witches are trying to give him a false sense of security with the visions they conjure. On the other hand, it's Macbeth alone who elects to pursue the path of murder that he becomes involved in, so he alone is responsible for his downfall. This is especially true after he chooses to have Banquo murdered.