[khafra]

1. If we find life very close to us, that does indeed increase the probability of the panspermia hypothesis.

2. The probability of panspermia will still not be 1, or even approaching 1. That leaves enough room to avoid "bullshit argument" in favor of "questionable argument," which is a caveat Bostrom (and Hanson, in his Great Filter) would happily agree to.

3. Even if single-origin life has seeded multiple planets, if the seeding occurred far enough in the past and widely enough, that still leaves us with an anthropic filter problem.

[Kliment]

I'm not seeing the "widely enough" in this case. Finding life on the one moon in the solar system that could support it, specifically finding life that is organic, would very much suggest single origin. The original Hanson paper sounded almost like it was actively avoiding that possibility. Thus my impulse to state it more strongly than is strictly necessary. Finding life close to us may increase P(panspermic hypothesis), but it increases P(common origin) more, and this ratio diminishes as we find life further and further away.