One of the annoying things about the whole situation is we have no idea of just how many resources are available to the Institute. For all we know, it has an infinite number of gen-3 synths available to do infiltration. And being perfect duplicates of existing people is NOT at all required. Pretty much every non-Institute group is looking for warm bodies to augment their ranks. So, if the Institute has one infiltrator unmasked, it is MUCH more effective than a gen-1 frontal assault to simply send in another infiltrator. And as the infiltrator presence is felt, the understandable mistrust that real humans have for one another is actually better for the Institute as numerous groups, communities and settlements start conducting increasingly vicious witch hunts, with the inevitable result that LOTS of real humans get killed in the crossfire. The end result is practically every community disintegrates as families decide it is healthier to just go it alone. Attacks by gen-1 synths, otoh, are so straightforward us-versus-them situations, it would actually help to unify community individuals. After all, how can you distrust someone of being a synth infiltrator when you saw him with your own eyes, gleefully dispatching synths? [Ignoring the logic that the Institute may very well be smart enough to program an infiltrator to do precisely that, to prove his bona fides as an actual human.]
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On a related note: So I was camped out at Sanctuary Hills, awaiting an attack that still hadn't materialized after more than a week. So I took the time get around to building a surrounding wall with only the one gate at the bridge. I also -- and I believe this is VERY significant -- removed all of the dead gen-1 bodies, along with the body of the infiltrator, and dumped them on the other side of the bridge. I then made a circuit of settlements by walking so I could build up a crops stockpile at Red Rocket. When I had enough to replace ALL of the plants in SH in the event a synth attack destroyed everything while I was absent, I fast traveled to SD-I and scooped up the crop surplus there as well. Then fast-traveled back to Red Rocket where I discovered that the "Help defend Sanctuary Hills" message had finally dropped off of the Pip Boy. Snatched up the crop stockpile and shuffled (seriously overloaded) to SH, dreading to see the extent of the damage. At the body dump at the bridge, only the dead infiltrator remained. At the front gate, I needed to repair ONE of the two turrets there. Other turrets in sight (6) were all still functional. Hmm. Shuffled over to the farming area and discovered NOTHING there had been destroyed. Dropped my burden in the Cooking station and surveyed the entire settlement. To my (pleasant) surprise, that was it: ONE turret damaged.
Hmm again. Could it be.... The devastating attacks people have been experiencing while they were absent might very well be because the "dead" synths were playing possum? Or spending time doing repair functions on themselves?
It was actually kind of humorous when a settler made the stock comment, "The Institute really got us good this time." Right; ONE turret decommissioned. May all attacks on my settlements be so "devastating".