I don't mind too much about arguments like unrealistic, poorly implemented or even unbalanced. There's basically just one (personal) argument: is it FUN to play? I've played this game since civ 1 and I'm still playing civ 6 (although somewhat disappointed), but for me the overall fun in playing civ has decreased by the 1UPT mechanics for only two reasons: 1. The AI can't handle it properly. It's not fun to watch an AI randomly shuffling units around. Has been an issue since its introduction in Civ V. 2. Moving units is a hassle. Even moving a 10-unit army from the east to the west of your own empire is not fun. My infantry unit can't move over my own roads because there's a missionary in its way. Not fun. Thers's plenty examples like this. For me, there would be an easy solution: allow multiple units per tile, but dramatically decrease (or even eliminate, see what works best) offense and defense power of a stacked unit, so stacked units can't be used in battles, but you can stack units for moving/transportation in safe areas.