Except in your ludicrous analogy, it's as if God were able to step in after the murder, point out that the murder was illegal, and then resurrected you. Sure, you spent some time dead (in jail/on trial), but afterwards you're free to go.
And it absolutely deters offenders, as prosecutors and cops aren't fans of failing to prosecute someone because they fucked up and illegitimized the evidence they planned on using.
I mean, sure, that particular cop got to laugh at your texts to your ex, but as far as evidence goes, it's a slam dunk for you.
Cops easily get around this with parallel construction. They illegally read your texts about you going to go pick up some drugs, then pull you over for "driving erratically" and "accidently" stumble upon the drugs you bought. The police do not care about your rights.
That's the kind of faith in the system that only people who have never seen it in action still have.
A friend got pulled over for speeding. Cop did not clock their speed, at trial they did not even know the speed limit for the road. Judge "seems legit, your guilty."