Precisely. If we ignore the 4th for a moment, the NSA doing this kind of surveillance wouldn't be an issue if it was only ever used to catch bad guys within the constraints of the law. But, as the DEA story shows, once this power is in the hands of corruptible people, they will take shortcuts, subvert the rules, and bypass procedure to get what they want. In their minds, the end justifies the means, and our legal system is specifically set up to thwart that temptation specifically because people are imperfect and corruptible, and will misuse the power they're given.

There is nothing so laughable as the people in government saying "We won't abuse this power, trust us" as if to excuse the fact that they got caught abusing their power, and demonstrating that they absolutely cannot be trusted.