Not surprisingly, Sandberg's contribution to the debate is unique and provocative. In his article, Inviting invasion: deep space advertisments and planetary security, Sandberg admits that it's hard to assess the risk, but that we might not like the answers:
There are two aspects to extraterrestrial risks: the probability that the signals will be received by somebody, and that we would (afterwards) wish the aliens did not receive them. Stephen Hawking argued that we should be cautious: to him the probability of aliens was relatively high, but he also thought the probability of them being risky was high...This risk might not be a direct invasion threat, but simply dangerous cultural transmissions: in the past some human societies have fared badly when in contact with more advanced societies. Even a radio signal might consist of an information hazard, for example containing infectious ideas or software. The aliens do not even have to be deliberately malicious: many humans would jump at the chance of converting non-believers to their favourite belief system, thinking they do them a great service.Ouch. And I'm sure Sandberg would agree that the boring answer is also very likely the most improbable answer--particularly given all the recent evidence indicating that the Galaxy may be teaming with Earth-like planets.
While optimists about SETI tend to think communications would be benign, it is hard to assign a probability to it. The only thing we can say is that we have not seen any alien communications or even signs of them, which suggests that aliens either do not exist, we are not receiving anything from them (e.g. they are too far away or we are listening on the wrong wavelengths) or they are keeping quiet.
From a species survival perspective we should generally prefer the middle answer. Why? If we are the only ones it means that either intelligent life is exceedingly improbable and we are lucky, or that intelligent life is not so uncommon but something wipes it out before it starts to spam the universe. Bad news. If there are aliens and they keep quiet, then they must have a very good and consistent reason. This could again be something positive or neutral (e.g. they are too alien to communicate, they all do not wish to interfere with us) or something bad (e.g. civilizations that remain obvious fall prey to self-replicating weapons). Only the boring middle answer - that we simply cannot communicate for technical or distance reasons - implies safety.