What is the difference between an encrypted hard drive, and one filled from /dev/random or the like? If I fill a hard drive with cosmic noise, can I be face consequences for not being able to decrypt it?
Nothing - my personal opinions aside, the difference seems to be if the prosecution has enough evidence to convince a judge that a specific piece of suspected evidence is contained in that encrypted data.
The court decision even addresses this - that there is no way to tell whether the drive is full of random data or real files once decrypted, and the government has not shown they are looking for a specific information - they are basically going on a fishing expedition saying "make him decrypt his drive because we think we'll find bad stuff on it"..... that's different than "Make him decrypt his drive because the file we gave him in the sting operation is strongly believed to be sitting on his drive, because the undercover officer saw him load it onto the laptop right before we arrested him". In this case, the court ordering the guy to decrypt the drive is reasonable. The devil is in the details it seems... the details are everything.
They absolutely can't just bust down your door and demand your decryption keys.... the court seems to have addressed that.