- Human society and culture has a natural inclination towards being a weirdness censor.
For example, let's say you saw a walking skeleton dissapear behind a tree. You look and there's no skeleton. Do you…
A: Assume you were vividly hallucinating the whole thing.
B: Assume someone is pranking you with a good-quality anamatronic, puppet, or some new holographic tech.
C: Assume you might have seen some kind of ghost, and maybe mention it to your friends when you hit the bar later that night.
D: Freak out because your entire perception of reality has been shattered, as there's now proof that all manner of things that go bump in the night exist and you were never truly safe.
For most of us, we'd go with options A through C. If we see something strange, we're more likely to pass it off as something that fits in with our view of reality than assume that reality isn't what it seems to be. If I believe in ghosts, then that skeleton was totally a ghost. If I don't, I may assume I caught sight of some sort of weird puppet. And if I'm into drugs, then I'd probably assume I'm on a trip, and will need to remember to either buy the same stuff again or swear off of it.
The last thing I'm going to assume is that it's a bona-fide skeleton that proves that what I thought of reality is actually false.
Note I'm speaking of this in the real world, where SCPs (presumably) do not exist. Now, in a universe where they do and are actively suppressed, there's probably not going to be too much of a difference in human society, aside from what we may see as a slightly higher-than-average belief in blatant supernatural things and events.
The Foundation wants to contain everything unusual. However, to maintain the illusion of "normal" reality, it just has to contain most things and remove most information to the contrary. From there, any slip-ups can be easily shrugged off by our tendency to explain something in a way that fits our existing worldview. Those smart/attentive enough to connect the remaining dots are likely treated the same way as conspiracy theorists are in our world- seeing too much in coincidences, possibly crazy, and not really a trustworthy source of information.