Truth is something that can't be measured, it has to be reviewed manually according to certain criteria. So there is no automatic method to determine the realism of a movie, people need to put a lot of work into it. You can find such information about mistakes e.g. in some movie reviews or in the goofs section of IMDb (namely Anachronisms, Character errors, Factual errors, Errors in geography). This so-called free Encyclopaedia also typically has details about popular culture and its mistakes.
David McCandless did a scene-by-scene review of the truth of a few movies. He used Unknown, False, False-Ish, True-Ish, and True as categories for each scene. You can find the result here and the raw data here.
So, yes, other people do care. Still, movies are economical entertainment products and not documentaries. Determining the realism is a lot of work that in detail is not justified normally. Find a few good movie reviewers / bloggers whose style you like and who put a general emphasis on this. Reading about inaccuracies in detail before watching a movie will, of course, lead to a lot of spoilers.