This argument sounds like it’s SSA-ish (it certainly doesn’t work for SIA). I haven’t personally looked into this, but I think Anders Sandberg uses SSA for his analysis in this podcast, where he claims that taking taking observer selection effects into account changes the estimated risk of nuclear war by less than a factor of 2 (search for “not even twice”), because of some mathy details making use of near-miss statistics. So if one is willing to trust Anders to be right about this (I don’t think the argument is written up anywhere yet?) observer selection effects wouldn’t matter much regardless of your anthropics.
This argument sounds like it’s SSA-ish (it certainly doesn’t work for SIA). I haven’t personally looked into this, but I think Anders Sandberg uses SSA for his analysis in this podcast, where he claims that taking taking observer selection effects into account changes the estimated risk of nuclear war by less than a factor of 2 (search for “not even twice”), because of some mathy details making use of near-miss statistics. So if one is willing to trust Anders to be right about this (I don’t think the argument is written up anywhere yet?) observer selection effects wouldn’t matter much regardless of your anthropics.