We are conscious carbon based organisms. So are cats and octopi. Without the chemistry of carbon as a foundation for the anatomy, consciousness could not exist. Consciousness is a process dependant on a physical substrate. Consciousness does not exist in a vaccuum. Said differently, "Mind is what brain does". Brains are built on a foundation of carbon and of course water.
UFO afficianados make an assumption that LGM must also be carbon based beings. This way, their conscious processes could conceivably align with the chemistry of human consciousness. The result of this similar chemistry is ultimately communication.
It is not the only possibility.
Imagine that consciousness could emerge from a different chemical foundation, perhaps silicon and vinegar. Would such beings be capable of perceiving and communicating with carbon based life? Would they even be aware of us, or we them? Would their science only probe their heavens for silicone based life forms which are capable of consciousness? Right now, the general consensus is that alien life must be structured around water. Our planetary explorations prioritize water as a prerequisite to life. We though live in the Goldilocks area from the Sun where liquid water abounds. Here is yet another variable. Must an alien arise from a wet world and be carbon based to achieve consciousness? That is a bit of human conceit.
One regular poster on the forum has criticized current science for not recognizing the possibility LGM have a physics which allows them to explore where we can not. That would perhaps also extend to anatomy and physiology. I wonder whether these different beings would be consciously aware of carbon based life in the first place and if so have any desire to communicate with it since the effort may not be worth the reward. We assume these others would have a need to know. What would mutilated beef taste like to an acidic silicone space traveller?
We have wrestled with this problem. There is the golden record attached to the Voyager space craft. The assumptions are that a conscious entity could retrieve and interpret the messages. We sent nothing encoded any other way because, besides expense and space requirements, we think our best shot at conscious communication is with those who are constructed as we are. We could be the exception, not the rule.
How could any alien in good conscience hurt the DP9?