To be clear, though, the Genesis account does not speak of sinfulness or imperfection being inherited. That's a Christian concept introduced by Paul. The only things being inherited according to the story itself were the specific curses on man:
Man:
- Enmity with snake (will have his heel bitten, now that snake is low to the ground without his legs).
- Ground will not be as fruitful.
Woman:
- "Sorrowful" pregnancy and painful childbirth.
- Enslaved to man through sexual desire.
And snake:
- Legs removed, and will now (literally, or perhaps poetically) be eating dust.
- Will get its head stepped on by man when it attacks, since it is now low to the ground.
But I agree with your basic reasoning point, EdenOne, namely that from both the Jewish and the Christian standpoint, God chose to design us a certain way which allows imperfection or a curse to propagate to each one of us. He could simply have chosen to not design us that way.