"Objectively evil" does not mean "really extra super bad." "Objectively evil" is a category distinction. The object of an action is what gives it its species, since the object defines an act as the form of a thing defines its species. Objectively evil acts are acts that can never be good because their species renders them incapable of it.
Acts that are not objectively evil can be rendered evil by the ends intended by the agent and the circumstances surrounding the action. A prudential judgment is involved in deciding whether or not particular circumstances render a particular action--one that is neither objectively evil nor done with the intention of achieving evil means--good or evil.
The point being that a person who is not in favor of some objectively evil act is not immediately morally better than a person who is in favor of some objectively evil act if they are in favor of some particular evil act or acts. It would depend upon how grave the objectively evil act was in comparison to the particular evil act or acts, as well as how prevalent the particular occurrences of the objectively evil act are.
This is not to say that one can vote for, say, a pro-abortion candidate because they are against an unjust war. But it is to say that arguing against this position is more complicated than saying, "abortion is objectively evil; war isn't." It depends on the gravity of abortion versus the gravity of the unjust war or wars. And this is without factoring in other important issues, like calling sodomy a basis for "marriage", torture &c.
The point is that "prudential judgment" is not a "get out of evil free" card. There is a prudential judgment involved in deciding whether or not executing certain criminals is necessary for the defense of the common good. This does not mean a regime can indiscriminately execute people and hide behind the idea of "prudential judgment" as a shield. The fact that a certain action is not evil in species does not render it acceptable to commit a number of particularly evil actions of this type.