Stealing food is clearly evil if you have no need but the victim has need for the food. If the needs are opposite, then it is not clearly evil. So there is no clear boundary, but what would a vague boundary require?

You are pointing to different actions labeled stealing and saying "one is good and the other is evil." Yeah, obviously, but that is no contradiction - they are different actions! One is the action of stealing in dire need, the other is the action of stealing without need.

This is a very common confusion. Good and evil (and ethics) are situation-dependent, even according to the sternest, most thundering of moralists. That does not tell us anything one way or the other about objectivity. The same action in the same situation with the same motives is ethically the same.