[hy3lxs]

It's an expected value thing. If the event is catastrophic enough (the Ur-Quan notice our radio signals and enslave humanity, or global warming destroys the ecosystem and we all die) then we should try to avoid it, even if the likelihood is very small.

[gojomo]

Aren't there positive outlier possibilities, as well?

Perhaps only contact will offer hope of asteroid or gamma ray burst defense, or escaping Earth before destroying ourselves.

[David]

Yes, but as a species we have a tendency for risk-aversion. So I think you have to set it up as risk versus risk, rather than risk versus benefit. Weigh the negative outliers on each side against each other, instead of weighing negatives versus positives. If we don't contact other species, what are the chances that we'll kill ourselves? (Global nuclear warfare, environmental destruction, what have you). If we do, what are the chances that they'll kill us? (Personally, I think it's quite likely that we'll end up killing ourselves, in the long run. That makes contact the better option.)