To some.. truth 'is' merely their opinion... to others truth is the opinion of others.. and to others truth is a matter of personal spiritual revelation.. My experience is truth usually is a matter of all three.. At its highest level..
At its highest level, yes. How often does that occur? Surely it does, but few would say it occurs often enough. As boop remarked just barely the other day, "No one can possibly know absolutely everything that is relevant to even a single simple problem." This is not an understanding unique to her, nor would she ever claim that it was. Boop was simply reminding us that truth is difficult to know even absent attempts to erect a barricade or to assert a monopoly. Your point, I think, is that knowing truth, even in the imperfect state we know it, demands a good will and a collaborative effort.
Necessarily so, I think . . . at its highest level. {8^)