Random people are going to be far less prejudiced than the people who would apply to be full time jurors.

The pay will no doubt be shit, so the only people who will apply to do the job would be people with no discernible skills, or people who are motivated by some biased agenda (“cleaning up the streets” by always siding with guilty verdict, or “defying the police” by always returning not guilty verdict, or even more complex types of bias). Anyone who has skills would sell those skills to a much much higher bidder.