But naturally, there significant limits on how much and how long each of infiltration be effective. A infiltrator from X sent to gain control of Y and gaining complete control there of will often identify with Y since leading it give them more power (Stalin was likely a agent of the Czarist secret police before the revolution but he probably wasn't taking orders from them in 1935 etc).

Read Stranger in a Strange Land, read about Hubbard and Heinlein's friendship, and look at the timeline of when Scientology started and Stranger in a Strange Land was published.

I mean, it shows how much intel agencies can "screen for high intelligence individuals" ?

The existence of a mailing list or something of that sort isn't particularly worrying. I don't think it's reasonable to expect a firewall between police departments and local businesses any more that it would be reasonable to expect one between PDs and local residents.

I would be alarmed if it turned out that Amazon was giving the Seattle PD direct, warrantless access to data about their consumers, or something like that. But there's no evidence presented here of anything particularly sketchy going on.