Here are my arguments, as many as I could think of (or heard from other people):

- There are thousands of laws and regulations, many quite vague in their application. Even the government can't tell their exact number. Are you sure you are not violating any of them?

- Even if you've done nothing illegal, if they really have to get you all they need to do is dig dirt on someone close to you. Are you still ok with mass surveillance? Everyone's got a cousin with a drug problem or something similar.

- If you want to plan a surprise trip to Hawaii for your spouse, is it OK to want to keep it a secret? Does the "nothing illegal -> nothing to hide" argument hold here?

- If you are a creative person, would you like your new novel or album to be leaked from your DropBox, Gmail or some other account to the world?

- Why would Apple hide its new products until the official release? Would it be OK for their trade secrets to be laid bare? After all, they are fully legal, thus, nothing to hide?

- If you are in business, bidding for contracts, would you like to have your communications observed by potentially rival entities?

- You have an email account with spam filters? They can label homosexuals, liberals, tea partiers and such just as easily as they label a spam.

- Do you use Google? Google makes use of a network analysis algorithm called Page Rank. In a similar way, Big Brother could rank people by their social influence (I believe FB calls its version 'EdgeRank'). They could get a list of "100 top influencers" in any social network. They could do that with the metadata from phone calls alone.

- Would it be OK for the government to know who's organizing protests against them? To have blackmail material on their opponents?

- Even with phone metadata alone they could see our social networks and movements. That would give them powerful inside information from what is considered mostly harmless data. It's not in each data point alone, it's in their aggregate that such information emerges.

- Is it OK for the government to monitor the communications of lawyers, doctors and psychologists? We entrust them with our most sensitive information.

- What will be the impact of mass surveillance on social activism? Don't we need to counter balance the government any more? Do we trust these guys implicitly?

- Information is power. Massive, asymmetrical information. They know about you everything, you know nothing about them or how they are using your info.

- In the future this database could be leaked and then you'd become blackmail-able by third entities. Imagine what the mafia would do with a database of people's secrets. If Snowden was able to get his hands on it and leak it, don't you think mafia could do the same? They could use a mole inside NSA to extract blackmail material. Hell, NSA might trade information on you with anyone if they get an advantage. Maybe NSA needs to place an informant using the mafia, while mafia wants some dirt on legitimate people and businesses to extract money from them.

- In the future all countries will (if they are not already) intercept their digital communications. The logic goes: everyone is doing it, so we need to do it too, otherwise we'd be at a disadvantage and not be able to defend ourselves. Imagine a world in which not just NSA, but hundreds of entities, national or corporate, have data on you. They could use that data for whatever interest they have. You could be indirectly targeted just for being associated with a certain person or company.

- Searching terrorists by statistical analysis of people's data doesn't work so well. The problem is mathematical: say there is just one terrorist in a million people. Even if you have a system that is 99.9% accurate, that means 1000 people flagged. That's one thousand false matches for one potential true one. Those people would then be harassed and investigated even though they are innocent. The system is bad in principle. It doesn't do so well on account that terrorists are few and normal people many. If you had a company that produced 999 defected products for every good one, would that be acceptable?