You brought up an interesting point regarding communication with ETI, one which has generated a lot of comment lately. Should we make an effort to advertise our presence (Active SETI) or should we restrict ourselves to simply listening for alien signals, (Passive SETI), for safety’s sake?
Our own history as a species suggests contact, even non-hostile intercourse, between different cultures often leads to tragic consequences for one, or both of them. Even if both contactees are determined to be peaceful, and if they have no physical means of hurting one another; they would still be a potential source of philosophical or cultural disturbances in the other. The older feeling (I’ll call it Saganism) is that the aliens would be so advanced that they would be morally and intellectually superior to us and incapable of causing us harm. The more modern response (lets call it Hawkingism) is that ET could just as likely be murderous xenophobes as kumbayah angels. I tend to favor that interpretation. These are aliens, after all, we have absolutely no foreknowledge of how they think.
It may be wise to not engage in any active SETI, at least until we have some knowledge of our neighbors. The usual response to this precaution is that “we’re already broadcasting our location and culture to the universe anyway using our TV signals.” This point of view is usually reinforced with the mental image of alien intelligences trying to make sense of Lucy and Desi Ricardo or “The Honeymooners”. The truth is our accidental transmissions would not carry far into the galaxy, they would quickly be lost in the background noise, and no receiver, no matter how sensitive, would be able to pick it up from the static. Only our microwave missile detection radars such as DEW or BMEWS would be detectable over interstellar distances, and even they are beamed only to certain parts of the sky, and for only the last few years. Active SETI is hard to do, its unlikely primitives like us would be able to pull it off accidentally. ETI would be much more likely to be broadcasting inadvertently, although I suspect they would be much more careful about what transmissions they leaked out into the cold and dark. They would know there’s no telling who’s eavesdropping.
By carefully picking the right frequencies, and concentrating our signals into tight, targeted beams, even our primitive technology is capable of sending out a signal clear across the galaxy, something that would be detectable by receivers of comparable sensitivity to ours. But someone would have to be listening when the message got there, preferably with an antenna pointed in our direction. No, passive SETI is the only way to go for us, hopefully we can pick up some industrial noise from a nearby star. This is what I believe the WOW! signal was in 1977, a chance intersection with a moving beam of 21cm emission, probably generated for some reason totally separate from communication. Since we only heard it once, there is no way to prove or disprove that; but that interpretation is the one that best fits the facts.
It is very dangerous to try and guess what the motivations and psychology of alien civilizations might be. And they will realize they are just as ignorant about us. For all we know, they may feel any intelligent species is a potential threat which must be immediately exterminated, even if they do not feel threatened by us at the present time. Remember, they have no way or knowing our technological capabilities or cultural motivations. They may have no moral or intellectual inhibitions about destroying us, they may not even recognize us as sentient. And they may expect the same from us.
When you look at it this way, the Fermi Paradox (Where are they?) is no paradox. Its exactly what you’d expect.