My point is that a large planet in the system reduces the probability of large asteroid impacts later in a star system's history. I didn't mean that it immediately removes all asteroids from a star system after forming.
True, but you need water rich asteroids to crash in the immediate phases after planet formation, and then you need life to develop. After which you need asteroids to not crash into the planet. Of course in the meanwhile, you need a lot of other things like formation of atmosphere, plate tectonics, volcanic eruptions, lakes sitting on geysers etc etc.
Basically things have to (not) happen in a series of steps for life to form, even if other things like a rocky planet being situated in the goldilock zone come true. This is apart from a lot of other factors, like not having a big sun etc etc.
All this suggests even if we consider 'Terrestrial mediocrity' to be true. Life could just very very rare across the universe, if not totally absent.
That's fair enough, the point I tried to make is: Statistically, we would expect our solar system to be average among solar systems that can support intelligent life, not among all solar systems (following the Anthropic Principle). Therefore, the difference we see between our solar system and the average star system might imply something about what kind of conditions make intelligent life more probable in a star system.
If we see that in all star systems we know that evolved intelligent life (even if there's only 1 we know of) there is a large Jupiter-like planet, and that's very atypical among star systems, that suggests that Jupiter might have increased the probability that intelligent life evolved here.
