While one side having a friend/enemy distinction and the other side not is certainly a major part, I think there is one more aspect at least that is at play here. And that is this deep-seated belief on the right that there is this nebulous mass of neutral third party observers who are watching the battle between right and left play out, and they will decide who they favor based on who appears to be the 'good guys'. They believe there is an observant audience to this battle and whoever can win over that audience will gain such a large mass of followers that the battle will be over and the one who got the audience on to their side will win by default. So the right is constantly trying to portray themselves as the noble and principled heroes fighting the good fight in the right way, betting everything on even if we constantly lose every single individual battle along the way, the manner in which we lose will eventually win over that audience and we'll win in the end because we were clearly the good guys.

It's utter hogwash of course, and absolutely nothing in history demonstrates that anything like this has ever been the case. Even if there were some third-party audience that hasn't chosen sides yet, history shows us that they can be won over simply through propaganda or handouts or fear of sticking out from the crowd. They're not choosing sides based on some esoteric moral stand, they're choosing sides for personal reasons like which one won't kill them, which one will give them more money, which one makes them feel better, and so forth. And that's if this audience is even paying attention enough to play a role in the battle. Which most of the time they're not. Hence the right's near fetish level obsession with 'moral victories' [read: real losses]. That somehow after enough Noble defeats and fighting the good fight no matter what, even if you lose, somehow in the end the universe will reward them with the final victory because they deserve it.