The point of no return!

What point is the point of no return in the tragedy of Macbeth, in terms of Macbeth actually being labeled as being insane? Well, the most obvious answer that someone would jump to would be the death of Duncan. After all, Duncan was the first one Macbeth murdered, and so people would probably assume it to be the point of no return. Macbeth has already committed a dark deed, and so he's done for, right? I wouldn't say that, though. I feel like rather than Duncan being the point of no return, the murder of Macduff's family is the point of no return for Macbeth. See, Duncan's death had a purpose, and that purpose was to further Macbeth's career and get him closer to his goals. It was meant to help Macbeth, but the murder of Macduff's family is simply cruel. They did absolutely nothing to Macbeth, and yet he gets them killed to hurt Macduff rather than simply going for Macduff himself. Lady Macduff even cries that she has done nothing to get in the way of Macbeth just before she is murdered, to make things worse, and it's true. She did nothing at all to hurt Macbeth or get in his way, and neither did her children. Forget Duncan's death, this has to be the point of no return for Macbeth - he's just killing people to kill people at this point in the play.