No defenseman is a problem when they're on top of their game. They wouldn't be in the NHL otherwise. The problems arise when they're struggling.
That's why Staal is our best defenseman. When he's struggling, he's still useful out there. When Del Zotto struggles, he's becomes Del Zaster. When Girardi struggles, he can be brutal. When McD struggles, he becomes invisible (which still is a clear notch above Del Zotto and Girardi IMO). Del Zotto's clear problem is his terrible decision making and risk assessment, when he rushes things, it's game over. Girardi's problem is he's not a good puck handler by any stretch of the imagination (hence why it's such a mystery why he's constantly playing on our PP).
Staal is our best shutdown D-man and still has some offensive game to talk about. He and McD are the only two D-men I consider untouchable on our roster. Girardi and Del Zotto can be traded for the right parts.