I'm certainly not one of those yahoos who agrees with the statement that you shouldn't need privacy if you have nothing to hide. Typically these people are the same ones who would condemn nudism but disagree that it's the same thing. Modesty is privacy practiced for the sake of other people.
The typical argument against giving the government the right to routinely violate your privacy, and it is a good one, is that once you have allowed them this right, you have effectively removed your ability to later overthrow that same government when and if it begins passing laws which violate your fundamental human rights - at least those which you aren't as willing to surrender as you were the right to privacy.
I don't think necessarily that this is the BEST argument against allowing the government to monitor your actions.
The government has shown itself to be extremely bad at protecting private information about its citizens whenever that information is collected on a broad scale. Leaks of social security number databases, home addresses and even disclosures of their own secret agents' identities have occurred just in the last 4 years. The government has given databases of hundreds of thousands of US citizens to private companies so that their TSA bullshit can continue to harass citizens who don't pay a handling fee.
Given their problems with keeping secret information secret, are you really comfortable having all information about your life and identity stored all in one place with millions of access points (for all the people who will be collecting this information?)
At present, your only protection from your fellow citizens is the relative obscurity of an individual life and the lack of profitability in extending the effort to get all the goods on a single person. The time expenditure and risk is too great to usually bother with it unless it is a personal matter or the person is very rich.
The larger the profit which can be acquired by a single successful criminal act and the lower the difficulty and risk in the operation, the more likely it is to be attempted. This is why people rob cash registers most often rather than individual people in our United States. This is also why more people rob cash registers than banks - the risk is lower and the ease is higher.
When you have a giant database containing salable information whose security is necessarily extremely porous given the large number of people who need access to it, you have a target which is worth hitting. Now I realize these already exist - the DMV and Social Services in most states have a fat computer network attached to giant databases full of all sorts of information about families.
However, this information is already stolen and sold; abusive spouses seem to track down their "better halves" far more often than mere chance and predictability would account for. DMV records and credit card databases are used by private investigators and insurance companies to track people down regularly.
Now imagine a database which might store the last 1000 phone numbers you called, or who has been sending you mail, or where you go on your weekends, the last time you had an oil change and where, where all of your known associates and friends live... Now imagine this information also tied to your name, date of birth, mother's maiden name, city of birth, social security number, name of your first pet make and model of your first car and city you purchased it in...
The government retaining information based on omnipresent surveillance does nothing to protect its citizens, but simply leaves them vulnerable to the depredations of whoever has access to these systems.
A low-level bureaucrat becomes obsessed with a young boy and starts stalking him, arranging for selective "noise filtering" of his own activities long enough to kill him in the breezeway of his apartment block.
A somewhat underpaid mid-level manager with skyrocketing mortgage interest begins selling information in small numbers on beautiful women living near predators - all off-the-grid by performing the sales quietly through channels outside the scope of governmental surveillance. He calls it a "dating service."
Another mid-level manager makes a living selling full ID theft packages to illegal aliens. Scans the recently dead list, writes down all the necessary information to make up a fake ID that will pass muster, sells them in bundles to a reseller, later you find out that your next-of-kin is living in New Mexico and has run up $350k in credit card debt before the estate has even gotten out of escrow.
All of these scenarios are altogether too plausible, and at present are nowhere near as easy to perpetrate as they would be in a total surveillance state. Worse, getting away with it would be easier in a total surveillance state. In a total surveillance state, it is believed on an official level that nothing escapes them - they know everything. Therefore they would not believe that somebody was successfully circumventing their process. Therefore whatever you were accused of must be true because nobody could have done it other than you.
It doesn't matter that the credit debt was run up after your son was dead; only he could have done it, so you still are liable. The person who killed your child in the apartment breezeway was dressed like you and about the same height, so it must have been you. You must have signed up for that dating service, our database is impregnable, these aren't stalkers, they said you contacted them first.
So maybe I'm overreacting, but I think not. I think that we shouldn't be afraid of what our government will do to us with the information they gather; we should be afraid of what our fellow man will do to us with the information our government will gather and then refuse to adequately protect.