But we're also not a threat - even if we did detect another civilization, we'd have no way to attack them.
I don't buy the Dark Forest hypothesis at all, but it's also just not particularly a factor for us at our current stage of technological development, any more than a stone-age tribe has to worry about Mutually Assured Destruction via nuclear ICMBs.
With that sort of logic, you might as well exterminate every solar system around, whether or not it shows signs of civilization or even eventual habitability.
