After alliances are made people are robbing carts more from their "allies" than from their enemies because of the 100% injury rate in allied territory. Other than that the 100% injury is fine when I'm defending them from attack, or when I rob a third party's carts. But specifically when I rob someone's cart within their own territory I feel like I should not have that advantage, ally or not.
If people want some no-death duels, just put that in (and for that matter allow it between the same faction too). Don't make them have to abuse the 100% injury robbery mechanic in order to have no-death duels.