Sincerity Alone Will Not Save

A widely celebrated Christian author has written :

"Faith in a lie will not have a sanctifying influence upon the life or character.
No error is truth, or can be made truth by repetition, or by faith in it. Sincerity will never save a soul from the consequences of believing an error.
Without sincerity there is no true religion, but sincerity in a false religion will never save a man. I may be perfectly sincere in following a wrong road, but that will not make it the right road, or bring me to the place I wished to reach.
The Lord does not want us to have a blind credulity, and call that the faith that sanctifies. The truth is the principle that sanctifies, and therefore it becomes us to know what is truth. We must compare spiritual things with spiritual. We must prove all things, but hold fast only that which is good, that which bears the divine credentials, which lays before us the true motives and principles which should prompt us to action."

Does the post modernist and 'politically correct' way of saying: "whatver is truth for you...", or "if that 'truth' is what you believe then that is fine with me but it is not what I believe", or "anyone can believe in whatever they like just as long as it makes them happy and doesn't encroach on anyone else's lifestyle or belief system"; actually benefit anyone genuinely wanting to know 'The Truth'? Truth can be hard-hitting and it may not be what an individual wants to hear. It may shake a foundational belief or it could rock a whole worldview or even create a backlash of anger and violence! Could people, willing to admit that they are 'searching for Truth', actually be willing to engage in a genuine dialogue of investigation or will their preconceptions and life-experiences steer their thoughts and opinionated direction? How can they recognise 'The Real Truth' when they come across it?

Is there 'Truth' and is there 'error' ? Do we have 'black and white' areas even within Christianity that seperates 'Truth' from 'error', or should we (Christian and non-Christian societies) be more accepting / tolerant of the 'grey areas' in the way that people interpret and express their 'beliefs'?

Is the author correct to state the above that 'Sincerity will never save a soul from the consequences of believing an error ' or is life on this earth and how humanity relates to each other here and now more important?

I see this as the difference between following heavenly counsel and the tainted wisdom of humanity floating out from the UN. How far should humanity go to protect the right to the knowledge of 'all Truth'? Why, in a world of UN sponsored 'free speech and tolerance' is the Christian voice like the author above, not heard, accepted or tolerated?

Over to your comments ...