I am entirely willing to believe that Chambliss is simply technologically naive enough that he doesn't even know how to ask the NSA if the enforcement is meaningful. He's also probably quite happy to take them at their word, despite all their history of using their own dictionary to define their words.
Never mind that it's not legal to read emails, except with a single court order saying that it's legal to read EVERYONE'S emails. Which I believe they have.
The main problem is the "business records" clause in PATRIOT must be found unconstitutional. If it is somehow constitutional, then there is no privacy.
That's true for the vast majority of law enforcement though.
The police have the technical ability to pepper spray you, or arrest you, or shoot you. It is compliance with policy and legal requirements that (generally...) prevent them from not shooting you, not a technical safeguard. It's policy/legal safeguards that prevent the local health inspector from arbitrarily shutting down your restaurant. NSA analysts get held to policy as well; there have been analysts caught looking up information on ex-wives, for example, and fired for cause, so while an analyst may have the technical ability to task PRISM inappropriately, it's not an unlimited ability.
Do I think that PRISM should have better technical safeguards on it? Absolutely, if only because it's easy enough to do, and the system is way more powerful than what a random county sheriff might have available to them. But I wouldn't read any more sinister connotation into the current level of safeguards; even nuclear weapons can be disabled by only 2 compromised missile techs, so this level of protection seems pretty ordinary for government work.
I think you've completely missed the point. The impression that a layman will take from Chambliss's statement is that it is technically impossible for the NSA to collect emails.
This situation is not the same as your examples like pepper spray because everyone understands that a cop with a can of pepper spray is able to use it or misuse it and no amount of legal mumbo jumbo will stop him in the moment. The naive - and intended - interpretation of Chambliss's statement is the equivalent of saying the cops don't have any pepper spray to begin with.