You have to walk the entire path from the presumption of innocence. You need reasonable suspicion to accost someone in public. You need probable cause to arrest, and conduct searches or perform seizures. You need some credible evidence to go to trial. You need a preponderance of the evidence to win most civil disputes. You need clear and convincing evidence when the results of a civil dispute may impose a heavy burden or curtailment of rights on one of the parties. Criminal trials require evidence beyond reasonable doubt.

Failing to propose a believable narrative for each increase in magnitude in the burden of proof may cause the entire case to fail in the US.

If you collect evidence on someone that would ordinarily require probable cause when that person should be enjoying the presumption of innocence, that evidence is inadmissible, as is all investigation that depends on it to proceed.

Parallel construction is taking theatrical steps ex post facto to defraud the courts into believing that evidence is not only admissible at trial, but also a reasonable basis for further investigation. If the FBI performs mass suspicionless surveillance on presumed innocent victims, finds evidence of a crime, then notifies another agency to contrive reasonable suspicion, then probable cause, to uncover the same evidence via a legally plausible narrative, that is kicking civil rights square in the teeth. Furthermore, it encourages otherwise innocent activities to be considered as reasonable suspicion, and promotes aggressive police tactics to manufacture probable cause out of reasonable suspicion, or bully people into providing consent or confessions. You get "judge dog" approving search warrants whenever the K-9 cop signals him to provide probable cause. And it combines with forfeiture to become even worse.

When "accidental discovery" evidence is admissible, that is a significant weakening of the public's protections against government, as it provides additional avenues for parallel construction, such as dropping a smoke bomb through a window and pulling a fire alarm, such that responding fire department personnel can notice "drug paraphernalia" and tip the police, who get a warrant based on the tip and conduct a search for drugs. This encourages obstruction of services to promote public safety, such as disabling alarms or blocking emergency calls. When "clean hands" evidence is admissible, one "dirty hands" cop--or a paid informant--just needs to pretend to be an anonymous member of the public to tip off the "clean hands" cop. My own non-judge opinion is that poisonous fruit is when one law is broken in pursuit of enforcing another, not just when someone's rights are infringed.