Let's suppose that alien civilizations are not so rare and can communicate with each other. Let's then suppose that these civilizations are very different, but each of them can be defined as "good" or "bad". The differences between them are such:
- "Bad" civilizations tend to attack neighbors as soon as possible.
- "Good" civilizations are not aggressive by nature, but can attack first when they feel threatened.
The share of "good" and "bad" civilizations remains unknown to each of them. Moreover, given the huge distances between civilizations, each of them can not even be sure about partners: if even they're describing themselves as "good", this may be the deliberate and very sophisticated misinformation. Everything you have is their words and, without face-to-face contact, there is no way to check it.
The last assumption: interstellar war is very short and, with other things being equal, attacker have huge advantage over defender. When your goal is total genocide and attack is carried out with a near-light speed, the victim just have no time to react or at least understand what's going on. In short, preemptive strike is key to victory.
Now, what conclusions can we draw from this?
Optimistic conclusion: yes, we don't know the share of "good" and "bad" civilizations, but we can assume that "bad" civilizations are more prone to self-destruction in internal conflicts. Therefore, the more advanced civilization we've met, the more chance this is a "good" one. In general, universe should be filled with old and advanced "good" civilizations living in peace.
Pessimistic conclusion: for any civilization, no matter "good" or "bad", the only logical behavior is to attack aliens as soon as possible. In ideal case, attack before other civilization even learned about your existence. Imagine two civilizations, A and B. While A already knows about B, B is still unavare about A.
- If A are "bad" civilization, they will attack and destroy B. Plain and simple.
- If A are "good" civilization, they are still not sure (and can never be sure) about B. Attempt to talk with B will not give the answer, it will only lead to disclosing itself. And this is very dangerous: if B are "bad", they'll immediately attack! Do not talk to B? Anyway, they will learn about you, sooner or later... The only way to ensure your safety is to attack first, as soon as possible.
- Even if both A and B are "good" ones already avare of each other's existence, they will still be very suspicious (remember, they can only rely on each other's words but can not check them). The worse, each of two civilizations will know that their very existence depends of other side who can press their own "red button" anytime they want. And the only possible way to ensure safety is... see previous item.
Therefore, if even all the civilizations are "good" by nature, they will attack and destroy each other at the first opportunity. This may be the solution of the Fermi paradox: actually, civilizations are abundant, they're just follow the only possible strategy: hiding from others and avoid any talkings.
So, what do you think? Where are the logical holes?