TLDW: Appelbaum believes it's better to defend your fifth amendment right than to lie (EFF agrees, Assange doesn't). And in areas of zero freedom, it's better to have the ability to give up your password (plausible confession -- my term) than to have the adversary believe that there's a hidden volume they haven't beat out of you yet.

There's more to this long running debate, but that's the gist of Appelbaum's position.

My take: Plausible deniability gives you the option to defend the fifth, lie, or give up your data, but your confession may never be plausible. Which is better depends on the sensitivity of your data and the willingness of your adversary.