Convicting the guy is one alternative, but there's another (non-mutually exclusive) option: punish whoever conducted an illegal search. If a warrant legitimised the search, punish the judge instead. If the judge didn't know any better because he was deceived, punish whoever lied to the judge, and so on.
"Might not get a conviction" is a negligible deterrent against police overreach.
But it isn't just that. It's a possible perjury charge for lying to a judge. It's the strong likelihood of ending the detective's career or at least limiting it significantly. It's the political fallout from articles like this one. It's the potential civil rights lawsuit bankrupting against the department and detective. It's the personal shame and guilt that the detective feels for knowing that it's their corner-cutting that let a murder escape justice. Imagine having to face the victim's family if this guy is acquitted...
These are big deterrents.
This is another reason why police officers should be required to carry malpractice insurance, that they pay for.
A survey conducted by the Innocence Project, Innocence Project New Orleans, Resurrection After Exoneration and the Veritas Initiative looked at five diverse states over a five-year period (2004-2008) and identified 660 cases in which courts found prosecutors committed misconduct, such as tampering with key evidence, withholding evidence from the defendant or coercing a witness to give false testimony. [..] Of the 660 cases examined, only one prosecutor accused of misconduct was disciplined.
> Evidence is merely a collection of facts, how it was gathered does not alter its factual nature.
That's obviously not true. The simplest counterexample is a witness report, where the credibility attached to the facts being reported will depend directly on the credibility of the witness. "The suspect verbally admitted he committed the crime while locked up in my car" will mean a lot less coming from a cop who lied to a judge while obtaining the arrest warrant.
It’s boring to argue about the definitions of words, but you’re using English and in the countries where English is primarily spoken, testimony is considered evidence.