They do have the ability to ignore laws, lots of government organizations ignore congressional guidance all the time and it only ever comes back to bite them if someone objects loud enough.
The US legal system doesn't "prevent" people from doing anything, we just punish violations and for those violations to be punished someone who cares about the violation has to be aware of the violation.
It's a pretty common meme in cop shows today that "We can't wait for a judge to give us a warrant - let's bust down the door" to which the audience cheers since bad guy is obviously bad, but that is illegal and, it can potentially destroy a case IRL - but only if the defense finds out the entry was illegal.
Not to be too inflammatory but there are plenty of cases where they ignore them without technically having the ability.
The hicks and the inner city crowd both mostly hate federal law enforcement.
The Bill of Rights doesn't permit anything, but rather lists certain inalienable rights held by all persons on U.S. soil--or so the story goes. The worry that it could be construed as a list of grants was extremely controversial.
The FBI isn't "less evil" because they "tolerate" laws that they have no ability to ignore. They aren't tolerating them out of the goodness of their hearts, or out of a sense of morality. If they had the ability to ignore them, they would.
Edit: Re: responses
I'm not claiming that the FBI is incapable of violating the law, I'm objecting to the parent's claim that they are somehow "less evil" than the Stasi because they "allow" the law to be upheld, when they're not the ones allowing anything. Yes, when they are able to get away with breaking the law, they sometimes do. It's not clear how prevalent this is, because "able to get away with it" implies not getting caught.