I just finished an Astronomy class...
We are protected from astral projectiles. As the come hurling at Earth, Jupiter casually floats by, grabbing the asteroid in its gravity well and pulling it off course. Every. Freaking. Time. This is because Jupiter is really close, has a massive gravity well that even affects our orbit, and because it will always pull approaching asteroids in a different direction unless it's exactly opposite of Earth (which is why we still get some major impacts).
Also, without a magnetic field, if we didn't crisp immediately, we'd certainly die off from cancer within two generations, or just pratfall ourselves to death due to our newfound lack of any balance whatsoever.