Hello Peterlag, perhaps I am misunderstanding your meaning and/or intent, but I can understand why our "religious leaders" teach what they do about our fallen nature, as there seems to be some pretty solid Biblical ground for doing so. For instance:
Psalm 51
5 Surely I was sinful at birth,
sinful from the time my mother conceived me.
Romans 3
9 Both Jews and Greeks are all under sin;
10 as it is written,
“THERE IS NONE RIGHTEOUS, NOT EVEN ONE;
11 THERE IS NONE WHO UNDERSTANDS,
THERE IS NONE WHO SEEKS FOR GOD;
12 ALL HAVE TURNED ASIDE, TOGETHER THEY HAVE BECOME USELESS;
THERE IS NONE WHO DOES GOOD,
THERE IS NOT EVEN ONE.”
23 for all have sinned and fall short of the glory of God.
Ephesians 2
1 You were dead in your trespasses and sins,
2 in which you formerly walked according to the course of this world, according to the prince of the power of the air, of the spirit that is now working in the sons of disobedience.
3 Among them we too all formerly lived in the lusts of our flesh, indulging the desires of the flesh and of the mind, and were ~by nature~ children of wrath, even as the rest.
For those of us who God has regenerated and made alive spiritually .. e.g. Ezekiel 36:26-27; John 3:3; Ephesians 2:4-5, we are commanded to set aside the old man/old self and put on the new man/new self, so in a very real sense, God has given us a new nature "spiritually", but all of us Christians were "by nature, children of wrath", as the Apostle makes clear for us, yes 
~Deut
Ephesians 4
22 You were taught, with regard to your former way of life, to put off your old self, which is being corrupted by its deceitful desires;
23 to be made new in the attitude of your minds;
24 and to put on the new self, created to be like God in true righteousness and holiness.
