But why is removing a player from a party for low DPS is somehow unjust if it results in inability to clear a duty?
Coil... yeah, whatever. Cloud of Darkness, Steps of Faith, Ramuh EX phase 2, Amdapor Keep HM, goddamn Titan... These all feature DPS checks that can easily lead to a group-wide failure when not met.
The game does expect you to perform well already, being bad isn't against the ToS but it is against what game actually expects you to do.
Sticking your head into the sand with "you can't stop me from having fun" is exactly what leads to 50-page threads like "Steps of Faith is too hard, QQ". It's just hypocritical.
I know this sounds a bit like "You don't have anything to fear if you don't have anything to hide", but developers chose to put the aforementioned DPS checks in front of the players, even those that don't do what is officially considered the raid.