I mean, If we shouldn't allow a juror into the justice system just because of their political alignment, then would the jury in every trial be just composed entirely of centrists rather than people selected by random chance? I will admit having a jury composed entirely of Leftists or Liberals might be politically biased, but is it any better if it's just the opposite side?
from the US Government :
Those qualified are randomly chosen to be summoned to appear for jury duty. This selection process helps to make sure that jurors represent a cross section of the community, without regard to race, gender, national origin, age, or political affiliation.