I often read that we must judge arguments or claims based on their own merits, rather than on the quality of the person presenting them. This is fine in realms such as logic or everyday life, where we can all have access to the relevant information, but how does this play out in complex domains, such as science?
For instance, suppose I am reading two books on the health effects of different nutrients, such as animal fat. One author claims all animal fat is harmful, the other claims that some animal fats, such as fish fat, is fine in moderation. Both cite studies supporting their views, but one author is a spokesperson for PETA and the other is a senior researcher at a well-known university.
As somebody who doesn't have access to biology laboratories to conduct experiments, and who perhaps doesn't have the time to read every source cited, critique every study made and read every attack made on both author's views, what is the best thing for me to do? Should I simply decide not to believe anything at all? It seems this is the only rational course of action, as to take a stand based only on two equally plausible-seeming books and two author biographies would be irrational. Yet simply saying "Oh well, I can't know for sure!" seems rather depressing.