There's a pretty big difference between targetting locations strategically and torturing / killing a prisoner that has already been rendered unable of doing you harm.
If you want to have an apt analogy, I say our treatment of Guantanamo prisoners and other "enemy combatents" that we've so labeled for the sole purpose of not extending them the rights of prisoners of war is the valid one. I agree that behavior is despicable, and it doesn't get enough attention.
Dropping bombs on combatants is absolutely fair game. It's not pretty, I don't like that we have to, but war necessarily involves killing people. Anyone purposefully bombing civilians is not ok (collateral damage is often unavoidable, but we must aim to minimize it). Anyone torturing or killing prisoners, civilians or otherwise, is not ok on either side.
The brand that doesn't lock farmers out will get more business, presuming that there is such a brand, and it makes decent equipment.
Otherwise used equipment will start commanding a better price. Plus new business will emerge in buying too-broken-to-repair farm equipment, and managing to rebuild it with better facilities and spare parts.
One of my more-fun tasks on the farm was going into the weeds to get three dead green-choppers and scabbing the parts to make one that worked.
The fun is that in 2001, the bright side of Iapetus was sculpted, with the monolith in the middle. In reality the dark side is sculpted from passage through the dust ring.
There's a bit more to it than that. My tops would be two points.
First, we're memetically infectuous. Plant a new idea here, and someone will run with it, most likely in some direction you never wished for. Many of our memetic infections are downright dangerous, lethal, destructive, etc. Contact might well be considered irresponsible, no matter how well intended.
Second, there's the thing I mentioned about our reverse-engineering technology. They might accidentally give us more capability than they wanted to. Not that we'd be any threat to them, but we've been sitting here for however long with the Doomsday Clock close to midnight. Give us something new that can be weaponized, (We've been able to turn just about everything into a weapon, perhaps the most resistant invention was the "death ray", the laser - it's had so darned many peaceful uses and has been very hard to make into aweapon.) and we will do so. Perhaps that weapon might be what tips the scale, ticks the clock, or whatever metaphor you like.
First, it doesn't explain Fermi's Paradox, it merely adds another term to it. In all of those various probabilities, apparently there is something like a 10% chance of not getting taken out by a gamma burst in half-a-billion years. I would also expect the odds to get better as a given galaxy "settles down", generating fewer big, hot stars and more smaller, calmer ones. Some neighborhoods are probably rougher too. I wouldn't wait around to settle Trantor, near the center of our galaxy.
Second, I wouldn't consider intergalactic contact in any serious way - the distances are bad enough for interstellar, do we really want to add a few more orders of magnitude?
Third, our presence establishes our galaxy as one of the more benign ones. There is at least one neighborhood that has been sufficiently peaceful for the last half-billion hears. Last I knew, there were no supernova candidates close enough to cause that kind of trouble any time soon, either.
Fourth, I'll focus on your word "silliness", which I think you meant as an understatement. There is conceivably a chance that we are under observation, and rank as "too silly" for any contact. The Earth has had an oxygen atmosphere for the last half-billion years, and we're on the verge of being able to detect other such atmospheres on other worlds such as Kepler has found. It's not a bad assumption that any civilization capable of interstellar travel is also better at planetary surveys than us. If they're there and within a few thousand light-years, they know something worth seeing is probably here.
At this point in physics we're stuck at the Standard Model. We have many theories that move beyond, but no facts to select among them, and many of the experiments would be incredibly expensive. But let's say one day we saw a "warp signature", it's quite possible that we could immediately discard half of those theories. (By "warp signature" I really mean physical evidence of truly advanced technology.) IF there were here watching us, and seeing our "silliness" as well as the scientific acumen of some, they would be especially careful that we see no such evidence.
Cars made of memory metals will spoil that one, too. Heat the wreckage to the right temperature, and have it spring back into a car.
No amount of careful planning will ever replace dumb luck.