I agree in principle with your two points.
First, we all should be aware of how our culture may have colored our glasses and created biases. Being aware of that doesn't change the fact but it may help us to react in a better way when someone says something that is totally contrary to our cultural upbringing. So although the Germans may have one culture, the Russians another, the British another and the Americans another, the truth is we are all blinded by this. Which is why we need everyone's perspective.
Second, calling someone a liar because you disagree with what they say and yet have no proof they are a liar is a very serious thing to do. First, as you have done it will be done to you. You have now given the green light for Satan and others to slander you with impunity. This is irrespective of whether or not your claim turns out to be true. Fact is you called someone a liar without proof simply because you disagree, hence that behavior will come back to you. But even worse, suppose you are wrong, they are not a liar. You are now one with the coverup, and you will be judged accordingly. There may be people who will be poisoned and damaged because of you and you will have to give account for that. We have been told that we will have to give account of every word we speak. Since these are two very serious offenses to our spirit one has to wonder how someone can do this and not have their spirit touched to repent of these sins? So yes, I agree that this behavior is not compatible with genuine faith. Yes, we are all sinners, but if you have genuine faith you would realize you had sinned and you would confess and repent.