In general, when we think about scientific inquiry, much of its power rests in the idea that everything is open to question. Turning a scientific gaze upon the world enlightens us and opens our potential to understand more deeply, while often challenging us to reconsider previously held beliefs and ideas. But science is not an unambiguously moral good.
Einstein questioned the ethics of building the atomic bomb. We know that research like the Tuskegee study of syphilis in African Americans has deep moral problems related to racism and informed consent. More recently, Stephen Hawking and others have raised ethical questions about whether or not we should engage in sending messages to the stars -- the risks of letting ET know we're here may outweigh the benefits of making contact if ET happens to be in a particularly foul mood when they answer our interstellar phone call.
Those opposing Active SETI or METI (messaging extraterrestrial intelligence) have a point. There could be some risk involved with alerting ET to our presence in the universe, although if ET has knowledge of physics allowing them to visit our corner of the galaxy, hiding probably won't do us much good anyway. If the extraterrestrials want to vaporize us, they'll go ahead and do it. More likely the extreme distances between Earth and possible other civilizations will mitigate against any real threat -- if we send a message out to a star in the Orion constellation today, it will take over 1,000 years to get there...
Perhaps a more important question is not about the risks of transmitting, but the dangers in receiving. Many in the SETI community have shown commitment to the belief that a technologically advanced civilization will be altruistic, despite the lack of evidence supporting that assumption. Therefore it is assumed there are no significant risks with listening quietly.
Maybe they're right. But even so, contact may prove quite dangerous to humans.
Why? Because of the potential to destabilize our civilization. How will humans react? Will there be panic, infighting, conflict? Imagine if the Chinese intercept the first message from aliens and want to keep the information they gain to themselves. How will the American and other governments respond if they think the Chinese might have information from ET about physics that would allow them to build super weapons? How will religious zealots, who are suddenly confronted with the idea that humans may not be so special after all, cope with news that we are not alone? Imagine if ET sends us an encyclopedia of information about themselves in which we learn that they are a civilization of card-carrying atheists.
And, perhaps, the most important question is what does sending a message say about them? One way to interpret this is to assume it means they want contact. But if they are significantly more advanced than we are morally (and there's no guarantee), perhaps they are also aware of what normally happens when more advanced civilizations come into contact with lesser ones. It's not typically great for the less advanced society whose culture tends to get run over, even if intentions are good on the part of those making contact. We have plenty of data to support this scenario from our own history.
Put another way, if ET is so advanced, shouldn't they have something equivalent to Star Trek's Prime Directive in which they make every effort to avoid meddling in the development of less advanced civilizations? Perhaps the very fact that they sent the message indicates nefarious intentions, or just plain stupidity, on the part of aliens who didn't give much thought to how sending might negatively influence the civilization at the receiving end, whose culture they knew nothing about when they sent the message.
Now, we need to turn this around to ourselves. Many scientists in the SETI community argue against METI on the grounds that it is dangerous. We should simply wait and listen until we are sufficiently advanced to deal with contact. We should hold off until we mature from our cultural and technological adolescence, whatever that means, to adulthood.
However, if we really think about it, the activity likely to be more dangerous to humans is receipt of a signal rather than sending a message. The way in which people will react on our socially fragile world is quite unpredictable. Awareness of the existence of another likely more technologically advanced civilization might propel our world into political chaos or it might have little influence. And we are left with the problem of what to think about an extraterrestrial civilization that sent a message without giving much thought to what it might do at the other end. Those aliens may be malicious at worst or naïve at best. Neither possibility is terribly good from our perspective.
The alternative, of course, is to roll up in a ball and hide. This seems rather pointless, since the genie is already out of the bottle, given the wide array of transmissions we constantly send from our planet. A society with technology 1,000 or 10,000 years beyond ours may well be able to pick up even the faint signals we are leaking out to the galaxy.
Instead of hiding, we should give a great deal of thought to the kind of message we might send and to what the possible consequences are of sending. By consequences here, I do not mean self-centered worries about ET blasting us, but other-centered concerns about how sending a message might influence or harm the recipient.
Perhaps the silence we have experienced to date is a product of more advanced civilizations saying, "don't send anything that way; those beings are primitive and we might ruin their development." If that's the case, then our only shot at contact will be METI as a way of alerting extraterrestrials that we are ready for contact.
If SETI scientists are right and ET is likely to be much older and wiser than humans, the real question is not the dangers of sending a message, but the risks of receiving one. It seems much less likely that messaging to more advanced extraterrestrials will have a significant impact on their society, while receipt of a message from advanced extraterrestrials might have a very significant impact on ours.