(Almost) every moral theory can be represented by a utility function

This was demonstrated, in a certain limited way, in Peterson (2009). See also Lowry & Peterson (2011).

The Peterson result provides an “asymmetry argument” in favor of consequentialism:

Consequentialists can account for phenomena that are usually thought of in nonconsequentialist terms, such as rights, duties, and virtues, whereas the opposite is false of nonconsequentialist theories. Rights, duty or virtue-based theories cannot account for the fundamental moral importance of consequences. Because of this asymmetry, it seems it would be preferable to become a consequentialist – indeed, it would be virtually impossible not to be a consequentialist.

Another argument in favor of consequentialism has to do with the causes of different types of moral judgments: see Are Deontological Moral Judgments Rationalizations?

Update: see Carl’s criticism.