Of course I wonder these same things. But when the consequences of becoming known to the wrong civilization are inevitable destruction, what are your alternatives?

We very nearly killed ourselves (we still might!) with nuclear weapons because we thought the other side might shoot first. This is that taken to an even further extreme: we won’t even know if we’ve been shot at until it’s far too late to do anything about it. We likely wouldn’t ever even know who sent the damn thing in the first place.

The balance of things is that silent civilizations with caveman-level technology are more than capable of wiping out noisy and naïve technologically-advanced civilizations.

You can wonder all you like about who and what these beings are and what wonders they must know of, and absolutely none of that will matter when a tungsten rod turns the planet into a fireball because you made the mistake of sending up a signal flare without having any idea that it was safe to do so.

One in a thousand civilizations could be paranoid enough to sterilize other spacefaring civilizations and it would be reason enough to be very, very quiet.

This is the presupposition that seems entirely baseless to me. An explanation has been constructed that comes to this as the only conclusion, but the assumptions in the explanation seem themselves to come from nothing. I think this is what often called "projection". Human beings are a violent creature that destroys others, so we assume these alien creatures must be. But they are aliens. We presently know nothing about aliens. My view is that we should interrogate the assumptions that lead us to your brutal conclusion. Projection of our own fears is insufficient to make the right choice.

Another question to reflect on: Why do you not destroy every person you come in contact with? They could likely kill you if they tried. But more so than legal consequences, you simply feel no desire to do so. There are reasons for your feeling that way.