remember that the left has no respect for the scientific method and most parrot "science" as a replacement for religious dogma. They have no respect for the constantly self-correcting disicipline that is science or any analysis that goes against the narrative^(TM). They only appeal to ethos and most simply do not understand that science is never settled.
Remember what based greek man socrates said, "I am the wisest man alive, for the one thing I know is I know nothing"
Bias is always present. The hope with science is that overtime you can root bias out of it and we do our damndest to eliminate bias(or uncorrupt scientists do at least). There's a reason appeal to ethos is the lowest level of evidence....Because humans are retarded and do stupid shit regardless of their degree.