As long as it is done to restore an ideological balance to the court that more closely matches that of the country I see no problem with it. Should we abide a partisan court that will hand down one unpopular ruling after another just to satisfy an ever shrinking conservative demographic? We should at least put the conservative court on notice that if they do another citizen's united decision that strikes directly at the heart of democracy or curtails in any way rights Americans currently have then steps will be taken.
Progressives only ***** about partisan courts when they aren't getting their way.
The only reason you don't like Citizen's United is because it added more players to the typical "outside money" game that is usually played by things like Unions, Thinktanks, and advocacy groups. Corporations didn't get special privileges, they just got what everyone else was able to do.