It's probably the word 'government' that's spooking everyone out. I think most people are conjuring up visions of the NSA telling insurance companies about your medical records and stuff. That or they probably think they'll be sending a SWAT team to your door every time you tweet about getting high or something. The point is, there are already checks and balances that exist to protect your privacy. Just because an organization has collected your data, doesn't mean they can look at it. Your metadata, no matter how much you try to hide it, is visible to a lot of people. Hell, your ISP probably uses that same metadata for all it's marketing and operational planning anyway. I personally don't think the US Justice system is so impotent that it cannot impose effective safeguards on the government.