I could never root for Pittsburgh. Ever. Not in football, baseball, hockey or rollerfucking. I won't be rooting for them on Sunday.
A Steelers win could directly help the Seahawks in the immediate future. In fact, the worse they beat on Arizona, the more Seattle may benefit.
Let's face reality: We can't possibly hate the Steelers any more than we already do. Another ring may make their fans and the media a bit more annoying, but that's it. However, recent history suggests that if the Cardinals win, they might get on a semi-roll over the next few years. Super Bowl winners have a strong tendency to at least make the playoffs the following season... Take a look at what these teams did the year after winning the roman numeral game:
2008 Giants: Lost in divisional playoffs
2007 Colts: Lost in divisional playoffs
2006 Steelers: Missed playoffs
2005 Patriots: Lost in divisional playoffs
2004 Patriots: Won XXXIX
2003 Buccaneers: Missed playoffs
2002 Patriots: Missed playoffs
2001 Ravens: Lost in divisional playoffs
2000 Rams: Lost in wild card round
1999 Broncos: Missed playoffs
Four out of the 10 Super Bowl winners missed the playoffs the following season, but look at the losers!
2008 Patriots: Missed playoffs
2007 Bears: Missed playoffs
2006 Seahawks: Lost in divisional playoffs
2005 Eagles: Missed playoffs
2004 Panthers: Missed playoffs
2003 Raiders: Missed playoffs
2002 Rams: Missed playoffs
2001 Giants: Missed playoffs
2000 Titans: Lost in divisional playoffs
1999 Falcons: Missed playoffs
8 out of 10 recent Super Bowl losers missed the playoffs the next year, and in most cases those seasons were absolute rock-bottom collapses... For whatever reasons, losing the Super Bowl tends to have a negative impact that lingers into the next season. Looking only at the Seahawks chances of returning to the postseason in 2009, we all might be better off if the Steelers beat Arizona's brains out... Maybe Warner retires or leaves as a free agent? Maybe the Boldin situation festers?
(You can't see it, but I'm wringing my hands in an evil manner)
Still, fuck the fucking Steelers.