The moon is so small compared to the arc of sky that we can be hit from that it provides no meaningful protection from asteroids or comets.
Better to keep our shield close to us to cover us from arrows, than to hold it far away, yes indeed.
I still recall them suggesting that was one of the Life-aiding aspects of the Moon in the TV show though. Just passing on the info.
It may be that they meant it in some way other than merely filling a large "arc of the sky" too? Something gravitational, or something to do with sweeping up debris near Earth (we can see by the craters how often the moon has gotten clobbered too)?
I've heard it say that having a giant gas planet like Jupiter sweeps up debris in early solar systems, sparing inner planets, and that's puny as far as filling an arc of the sky goes. (I was reading about TAU CETI for a thing I'm doing that suggests the same):
Although no planets have been detected orbiting Tau Ceti as yet, it is likely that any planet found to orbit within the star's dust disk would experience
relatively frequent bombardment from asteroids and comets of the size that is believed to have wiped out the dinosaurs and other types of multi-cellular life on Earth. As a result, some astronomers have speculated that it is likely that with so many large impacts, large and complex forms of Earth-type multi-cellular life may not have had the opportunity to evolve and persist on inner terrestrial planets orbiting this star. Others (such as
Glenn Schneider of the University of Arizona and
Scott Kenyon of the Smithsonian Astrophysical Observatory), however, argue that
a giant planet in the system could gravitationally deflect comets and asteroids away from inner planets that may support life in the liquid water zone, in the same way that Jupiter protects Earth in the Solar System.
http://www.solstation.com/stars/tau-ceti.htm
I've also read that Jupiter is a main
culprit in disturbing and throwing debris
at us from the asteroid belt.
It's a complex and dangerous Universe.
But I recall the main thrust of the show was:
Without the Moon, our earth would have been much less favourable to Life as we know it.
Without re-reading the thread, I think I saw and I'll risk repeating that the gravitational effects of giant outer planets can keep their tiny frozen moons hot and bothered enough to allow for liquid water, and heat the moons via gravitational stress.