I'm incredibly skeptical that that's really legal

Basically, if someone tried to press charges, it would come down to a court decision. For things like "stealing someone's trash to spy on their confidential correspondence in ways relevant to the highest levels of government," there are just sooo many crimes and/or torts you could potentially be committing, and beyond statutes it's probably a matter of common law

1) Ultimately it's a matter of predicting how a trial will go, so "this is legal" is always a probabilistic claim (though sometimes the probabilities are near certainties) 2) There are so many angles to attack this from, and a judge only needs to rule against you on one charge for it to be "not legal," so the odds stack up 3) Judges aren't stupid. If you feel the need to tell everyone that something obviously illegal is technically legal, you're probably not acting in good faith. "He's just using a loophole to dodge the system, don't let him get away with it" is in fact a legitimate legal argument

Rifling through garbage is actually legal (at least in some jurisdictions, if done correctly), but the motivation here is so ethically dicey, and the people you're doing it to are so particular, that I just don't think you can claim to predict how that trial would turn out