you need us to come up with an argument, find a reason for you, to justify why this is wrong? if you can't see why its wrong than why are you complaining?
i do believe this is wrong on many accounts, but it should be pretty straight forward as to why...but im feeling generous so try these :
1)If you wanted to set everyones lineup every week, than why don't you play in a league where you own all 10/12 teams?
2)I bet you wouldn't have done this if I was a team facing you and could put you out of the playoffs.
3)Thats part of playing in a league with people, they have their own idea's about the "best players" for the week are.
4)Since I(you) think that you(commish) don't have the best players in, is it ok if I change your lineups?
5)Being the commish doesn't give you god like powers (ala determining if a trade is fair, setting an active owner's lineups w/o permission, etc)
oh and my favorite...
6)If this isn't corrected I'm going to drop all my players and then quit the league.
Use #6 with caution. Friends or relatives may look down upon you in the event you screw up everyones season.