However, almost every drunk driver (not involved in an MVA or PI at least) tries to justify their actions by the same logic: if I hadn't been caught no one would have known and no one would have cared.
Here, we are only talking about a feeling of disgust one has after learning of what happened. The only harm here is the knowledge that it happened.
Again, one could make that argument about any public lewdness. If nobody happened to look there would be no harm. So using your logic no one should be punished.
Furthermore, as noted previously, the entire point of this stunt was the recognized risk of getting caught. Therefore it is rather disingenuous to argue that it would have been okay if they hadn't been. That was pretty much the point.
How could it have been lewd? They're "lovers". [Still not able to believe Biker said that.]