What fault does Malcolm claim to have?
Malcolm runs through a litany of vices, each one being more serious than the next.He tells Macduff that there is no limit to his vice--that he has so many that he'll make Macbeth look "white as snow" in comparison. According to the Great Chain of Being, the king, being closest to God, should be morally superior. (The King of England, mentioned earlier, epitomizes this righteousness when he is said to lay hands on the sick and heal them iv 3 155). One by one, Malcolm lists the kingly virtues that he supposedly lacks, saying he is intemperate (lustful) and avaricious (greedy), and that he lacks all kingly virtue (see list:lines 103-6.)The real issue for Macduff, however, is what Malcolm says he would do if he had power. If the rightful king rules, the great chain should stand and order should prevail; however, Malcolm says he would do his utmost to destroy the peace rather than keep it, and to create chaos instead of order.
This claim is what makes Macduff say Malcolm is unfit to govern (or live). Macduff does not wish to join him. In fact, he says that there is no hope for Scotland, and no reason for him to stay (he says that the prospect of Malcolm's tyrannical rule following Macbeth's has "banished" him from Scotland.)"
In Act Four, he actually claims several vices that would make him a bad king, lust and greed two of biggest. He doesn't really believe that these are his character traits, though. He is testing Macduff's loyalty; something that is intelligent considering the hostile state of Scotland at the time. Macduff answers that Malcolm is still the rightful heir to the throne regardless of his character faults. At this point, Malcolm confesses that he was testing Macduff and they continue to build the army against Macbeth.
1) His over ridding sexual desires that would not be satisfied even with all the daughters, the wives, the maids and the old ladies in Scotland.
2) His vaulting and uncontrollable greed for more power and posession, that would include taking jewels, and land from all his nobles.
3) The fact that he posessed none of the 'kingly' qualities- courage, fortitude, bounty, perseverance, paitence, mercy, lowliness, grace, devotion, jective, verity and temperance.
In these respects he was apparently a threat to Scotland, one grater than the tyrannical Mabeth himself, an unworthy heir to the throne, a man not fit to live and an unworthy son to the great King Duncan.