Don John, in Shakespeare's Much Ado about Nothing, is not fairly treated by critics and readers alike. His actions are, perhaps, acts of villainy but they can in some ways be at least understood, if not justified. He is man robbed of rightful social position by conditions outside of his own control, and thusly, he reacts violently and with great force against those who he feels have taken his rightful position. This not a great villain but man forced into an undesirable condition and thusly he rages against a world aligned against him.
Don John's actions are taken out of a plain desire to do evil but instead in a Machiavellian move to gain power. If you not that he strikes at only the powerful, Claudio, the prince's right hand in order to gain position and power. He does this by a manipulating the powerful in a manor such that they come to false conclusions.
This will enable him to come to power by right of ascension to the position his brother held. It may also be noted that by causing Claudio to dishonor Hero, he sets Benedick against him, Benedick being the superior fighter would have killed Claudio. This would have caused by reason of honor Don Pedro to dual Benedick. Benedick being younger and faster would also have defeated him, leaving Don John as successor to the throne. This would have put him in what he felt was his rightful place of power and authority instead of being his brother's charity case. He rightly feels that he belongs in a position of power based on his intelligence and ability to get what he desires done.
It must be noted that Don John is the half brother of Don Pedro. This puts him in an awkward social position...