The problem with the FBI/NSA mining their communication "for criminal activity" is that they probably don't do it exclusively for that. After Snowden we found out that sometimes NSA employees would use this snooping to stalk people they wanted to be in a relationship with, spy on their neighbors and other such unsavory things.
The other angle, besides just personal abuse (Ala loversgate), that far too many people fail to consider is this:
If the executive branch has such ubiquitous surveillance powers, given their history of manual blackmail and compromise operations, they are highly likely to seek to expand those blackmail style ops to a level heretofor impossible, essentially removing some of the last vestiges of the already under attack principle of seperation of powers and the checks and balances system which is a foundational part of the intended American political structure.
This happens yes. When I send my tax returns in the mail directly to the IRS, even if months late, the same week I start getting scam calls. So someone in the IRS sells that data. Though I doubt it is on an industrial scale, more like bad actors within these organizations, so a small percentage.
So I find articles about privacy that raise concerns about the NSA/FBI, have the effect of just deflecting and dampening where our concerns should be really focused.
Also we have already built and running mass-oppression infrastructure which could be used for incredibly evil things as soon as someone high up in the executive branch (or congress if they passed a law) said so. Makes us incredibly insecure in the event of a dictatorship-type overthrow
And even if it was solely for criminal activity it would still not be good. After all a lot of victimless "crimes" were, are, and will be illegal in a lot of countries.
