If mass monitoring in its current form is so good at discovering bad things AND if the information is allegedly not an intrusion of privacy, then make ALL of the tools and information immediately available for public use. The public will be able to find the bad people much more quickly than any agency because there are more of us. All allegations would have to be reviewed anyway, so no bad things will happen. PLUS, the system could be used to find torts and contract violations which would make the world a better place because bad people would not be getting away with breaking the law.
Making this argument will only convince some people. To demonstrate the truth of this statement, it would be great to build a real tool that tries to duplicate the NSA tools as much as possible. If limitations are necessary because of laws, then why do those laws not apply to the NSA? If limitations are necessary because of budget, then limit the targets to people in the federal government that are associated with the program, elected officials, contractors of the program, and proponents of the program.
Radical idea: offer a way for people to volunteer to be monitored so that all of their metadata can be collected. Especially offer it to people who say that no one should be against the surveillance. If people volunteer, then the quantity and quality of the data would dramatically increase and look more like the real database. Other people would also see how monitoring one person impacts dozens of people.