I'm far from saying for sure that something like that is definitely true, or even more likely than not. But it seems reasonably cautious to me to not arbitrarily broadcast out to the universe our location and rough technology level. We have no idea what might be out there or what its capabilities and thought patterns might be. Or rather, it seems hopelessly naive to me to just go ahead with such broadcasts, confident in our theories that nothing could possibly go wrong.
Regarding the Berserkers, it sounds a bit like a grey-goo scenario with self-replicating machines that wipe out all life. My personal feeling is that these scenarios are unlikely. If it were possible, it would have happened already... but it would be interesting to hear more systematic discussion of this point.
With my brief googling, I've found it pretty difficult to find anything on real "cosmic sociology". The research work I've found has mostly focused on human colonization of other worlds. I feel like it would make fun reading if there's anything out there.
That's pretty much the idea, yeah.
1. Destroying a civilization isn't risk free. If you destroy a nearby star system that harbors life, you better be sure that your weapon can't be traced back to you, by either any observers, or by the survivors. (See Forge of God & The Anvil of the Stars[1] for a study of the latter.)
2. If you do subscribe to the Dark Forest game theory, and do have what you believe is an untraceable weapon of some kind, there's no reason not to sterilize every star system around you. Why would you wait until you've detected life? Send out self-replicating Saberhagen Berserker[2] probes and sterilize the galaxy. (Be sure you've got a good Friend-or-Foe system in place.)
[1] https://www.goodreads.com/book/show/464609.Anvil_of_Stars [2] https://www.goodreads.com/book/show/582675.Berserker