>For any given matter of fact there is only one truth and unlimited falsehoods
For simple things, yes. For most debated things in society, no. Or at least, not in any knowable fashion. Whether a single payer system is better than a private insurance system is not something you'll ever reduce to a fact, because of the sheer number of variables, and even more importantly, because the notion of "better" is nebulous.
And as someone else has already commented, mainstream opinions on the same topic can differ widely from society to society (healthcare, public vs private services, etc). As someone who has lived in fairly disparate societies, that alone is reason enough for me not to put too high a value on mainstream positions in any society, since I know that if I did, I will often be "wrong".
And then there is the reality that there have always been mainstream views that conflict with science.
Not to take away from your wider point. Yes, I agree that one needs to have fairly good analytical abilities, and the average person often goes wrong when straying from the mainstream because it's easy to fall into "local" logical traps. However, I do think that at times one recognizes the mainstream to be one of those logical traps. In my experience, both elegant and simple ideas have a way of gaining hold in society - particularly in philosophy (think Kant's Categorical Imperative, or the Golden Rule), but reality rarely yields to simplicity and elegance.