During jury selection, the prosecutor and the defense attorney get to interview each potential juror. Both the prosecutor and the defense can eliminate potential jurors based on their answers. I believe they are allowed an unlimited number of challenges "for cause" and a limited number of challenges without cause.
If a juror stated that they believed that the word of law enforcement were always true, the defense attorney would almost certainly challenge them for cause, as that is clear bias, and they would not be selected for the jury.
In practice it's a balancing act, where the prosecution wants jurors who trust law enforcement and the defense wants jurors who are skeptical of law enforcement.
It is illegal to punish a juror for the decision they make during a trial. This is often referred to as "jury nullification" (or rather, is an important part of jury nullification).
If a juror stated that they believed that the word of law enforcement were always true, the defense attorney would almost certainly challenge them for cause, as that is clear bias, and they would not be selected for the jury.
In practice it's a balancing act, where the prosecution wants jurors who trust law enforcement and the defense wants jurors who are skeptical of law enforcement.
It is illegal to punish a juror for the decision they make during a trial. This is often referred to as "jury nullification" (or rather, is an important part of jury nullification).