Parallel construction is a completely normal and legitimate process. People who use it like a spooky term akin to "enhanced interrogation" or "extraordinary rendition" are just loudly signalling they have little firsthand knowledge of law enforcement.
I don't think arguing against the legitimacy of the investigative means used to acquire evidence is ever an admissible argument by which to contest that evidence before a jury. If those investigative means were a poisonous tree, that's an argument you make to the judge to preclude admission of that evidence in the first place, before either side gets to contest any evidence.
I think lawyering over whether parallel construction is lying or not is tactically silly. You'll be on much firmer ground arguing that parallel constructions completely undercuts the point of the "fruit of the poisonous tree" doctrine, which is to disincentivize illegal means of investigation.
Withholding evidence from the defense is very incompatible with our justice system.
Is this your best effort attempt at assuming good faith?
> "parallel construction is inadmissible evidence laundering."
Well, it's concealing a source, which is what I said. If you have an informant who's life would be in danger if they were revealed, then anything they tell you would have to be paralleled. There's nothing illegal about their evidence, they would just never testify to it.
Your position seems to be that there are legitimate reasons it was introduced. I don't disagree with that. That doesn't mean that the process doesn't involve lying in court to deprive people of their rights.
You say "conceal a source" but that is precisely depriving the accused of their explicit constitutional right to be "confronted with the witnesses against them".
(I will note that I've definitely been speaking with a US focus - not all of my comments will generalize.)