Why is the sin nature inherited?

[Drich]

...Actually no. Adam and Eve would still be running around naked. Without knoweledge of their nakedness, no babies.. (as it was before the fall)

Wait, so if "knowledge of nakedness" is necessary for reproduction, and this knowledge only comes once sins enters the world, then is sex sin? Something God designed is inherently sinful? Is that what you're implying?

Apparently in God's "perfect world" there would be no sex?

How many children did Adam and Eve have while living in the Garden?

Why? Because there was no need to reproduce and repopulate if they lived forever.

If you note Cain and Able did not come after the fall.