This is exactly right. And even in many many cases where they have been shown to know they were actually violating it they have immunity too.
https://ij.org/press-release/supreme-court-refuses-to-hear-c...
Out. Of. Control.
We emphasize that our decision applies only to suits for civil damages arising from actions within the scope of an official's duties and in "objective" good faith. - Harlow v. Fitzgerald [1]
Consider, in carrying out his official dutues, he has some degree of discretion in doing so. For example, some engineers might decide the best tool for their job that day is a slide rule. Others might decide on a given day to use an autoleveling level. And some, particularly Mr. Large, might decide on exercising the "detain trucks that are interfering with road work" provision. It turned out there was no such provision, and Large's job didn't have the authority to detain vehicles. But the absence of a statute specifically forbidding state employees (other than police officers) to detain trucks meant that he was entitled to qualified immunity.
Keep in mind that QI doesn't mean that the injured party isn't entitled to damages at all, it just means they have to sue the state and not individual officers/officials. Of course, suing the state has its own hurdles. Some government bodies have very short statutes of limitations for filing lawsuits against them, and they must receive advance notice before the claim can even commence. And the claim might need to be filed in a special court. And the state may be protected from liability if it had no advance knowledge of a condition, or by a statute limiting the amount of damages.
If I make that mistake as an ordinary Joe, how much time would I spend in jail?
I won't pretend to be an expert---today being the first day I've read about it---but, the very first Wikipedia article I read about the topic discusses qualified immunity w.r.t. "government officials", not "officers", which is a much bigger category of people. [1]
Because it's useful to have the enforcers of state power to be above the law.
It's a bigger problem for police officers than the clerk at the DMV, because one of them walks around with a gun, a nightstick, and a pair of handcuffs, and extremely broad discretion for their use.
Police officers just stand out because their actions can have much bigger consequences and they often act as individuals. But I don't think it should mean QI cannot exist, just that there should definitely be a different standard when it comes to life and death (or freedom in case of arrests).
Police are expected to be the security force of the powerful and influential against society's undesirables. If cops were required to strictly obey the law, they would be much less effective at this job. Most officers would understandably opt simply not to get involved in situations which might lead to someone's rights being violated.
If the powerful want a force which is willing to knock heads for them, they need to assure that force it will not be held responsible for the mess it makes along the way.
You're describing the principle of qualified immunity, which is already in effect in US courts. I was suggesting an explanation for why this is the law of the land, despite it being in such obvious contrast with the principles of a free and democratic society.
If you don't agree with my explanation, I'd be interested in yours: why do you think cops are exempted from having to follow the law the same as other civilians?