Excellent point.
By reading the Word of God, we know that all men are fallen and will deny His absolute truth, unless and until God turns them from the darkness to His light.
And this truth plays out before our eyes every minute of every day.
Read the Bible. It will answer your questions. There is no truth without it.
I do not know or believe that all men are fallen. I believe we are as we are, good or bad.
It is easy to say that man has fallen, when your reference describes fallen behavior as the behavior that man has exhibited since the beginning of time, but many do not use the same reference as you.