I don't have that much of a problem with this because the warrant is needed in order to actually do anything with the information. Also, to be precise, it's more as if the USPS scan the mail sender/receiver info (metadata after all). No content.
How do they stop him? It sounds like "can't access the data" means "the rules say he cannot access it, and if he is caught he'll get in trouble." Given that the people we are talking about think in terms of "the least untruthful statement" they can make, I would demand as much detail as possible.
"I don't have that much of a problem with this because the warrant is needed in order to actually do anything with the information."
Today a warrant is needed. Tomorrow, maybe not. What if tomorrow, the law changes, and the government starts hunting down anyone with leftist leanings? The first thing they'll do is query the database.
Laws are not sacred. Laws can be ignored or changed at any time. When we have to worry that the list of people we speak with today might be used against us tomorrow, there is a chilling effect on free speech. That is the danger of these databases. It is not enough that the data is held but can only be touched with a warrant; the data should not exist without a warrant.
If you think that's a possible reality you're living in a paranoid lala land - which isn't surprising given all the apocalyptic narratives we get from the media (gov't turning evil, zombies/robots taking over, evil agencies controlling the world).
The reality is that no wealthy democratic government in the past 50 years (some of which are less obsessed with protecting liberties) has slid back into tyranny. There are statistics that indicate that past a certain GDP threshold tyrannical governments become unsustainable.
This kind of thing is simply never going to happen.
When you start looking more than 50 years into the past you need to realize that this was a time when people thought blacks were lesser people than whites, women couldn't vote, many people were illiterate, people didn't have access to information, and maybe most importantly people were much much poorer (just look at the GDP). Now a days people for the most part live comfortable lives, and what we think of as "hard times" now is not the same as before (where it would often mean starvation for a large segment of the population) So to think history will repeat itself seems to me very simplistic.