There are roughly ~1 million LEOs in the US.
99.5% of those LEOs will NEVER have to fire their weapons in the line of duty.
Only .5% (or roughly 5,000) will engage in a gunfight or have to fire at a threat, and of those only a small handful are actually "illegal" shootings. If a cop does an illegal shooting (such as Officer Michael Slager) then YES, they deserve to go to prison.
I'd like to know where you get your statistics, and whether you're comparing like with like: while there are in excess of a million law enforcement officers, most of these aren't police. As for the number who have to use their firearm, that sounds unfeasibly low given the number of people shot per annum (but as these statistics don't appear to be officially recorded, it's rather hard to be sure).
That police today are taking a lot of flak, probably more than they deserve right now but IMHO not disproportionately, has a lot to do with old habits not catching up with modern technology: historically there have always been policment who've thrown their weight around, bullied and abused their power. The reaction of their colleagues and the authorities to this being discovered has typically been to cover up and pretend it didn't happen. Today that reaction is not just useless, it's positively counterproductive as evidence of misbehaviour is so swiftly propagated.
We, the public, need to understand that individual police officers do make honest mistakes & not indulge our lynch party mentality when mistakes are made.. though the police need to acknowledge when things go wrong, rather than pretending that they haven't or it was all the other guy's fault.
This isn't only happening in the US, there has been a similar erosion of trust in the police here for very similar reasons. Though not quite as extreme, helped by most UK police not being armed & so far less likely to shoot the wrong person.
But trust, once lost, takes an awful lot of work to get back. Sulking in ones car isn't exactly conducive to that.