"Asshole" was used in contrast to being "too ethical", so from the context it cannot mean anything except for "unethical". If the parent meant "asshole" in the conventional sense (e.g. parking in two spots) it would make no sense to bring up in this discussion.

The parent is rationalizing unethical behavior by classifying it as merely assholish. If you read the post carefully you can see the point where the cognitive dissonance takes place. The parent even said "the other extreme" is being too ethical, so he's clearing arguing that acting too ethical is undesirable.