Consequentialism is a theory of moral development which maintains that consequences to actions form the basis of the right and wrong of those actions. In other words, the outcome of an action determines the morality of the action. Consequentialists' problems revolve around the need to define what is good and bad before an action can be assessed. Otherwise, consequentialism commits the falacy of begging the question.
Also, the problem here is that who decides if the results are good or bad? Contrast with deontology.