This is slightly different from another well known phenomenon: the mixing of good and evil.
But here I am referring to the fact that the Evil Side is actually attracted to people and places and other sources of holiness.
For gentiles I am not sure how they could become aware of this phenomenon and protect themselves from it --but at least in the Jewish world I think this is a well known fact and so people tend to look at the good in any particular tzadik or holy place and when it comes to the question of mistakes or bad influences, they tend to ignore it and attribute it to this phenomenon.
[I think many Christians are aware of the problem with churches teaching a mixer of good and evil doctrines. But that is totally different from the phenomenon that I am describing here in which actual evil forces are attracted to places of holiness.]
I might try here to give a few examples. But before I do let me present a caveat. There are lots of times when I go with logic and label a certain movement or person as good or holy, and then through a combination of study and experience I discover I made a mistake. So I admit that the most powerful insights I have to the nature of the human world are based on experience and not logic. And this experience is uncommunicable to others because others can always doubt one person's experiences.
Be that as it may I think I have been able to identify places and teachings that communicate holiness to people and also to identify movements and people that communicate uncleanliness and evil to people. And I believe this is an objective assessment--not subjective--because like I believe in objective morality I also think there is a realm of values that are objectively holy and other values that are objectively unholy. And this does not depend on the observer but on the nature of reality itself.
In Israel I saw an opening to Being itself. But that seemed to have been temporary because at a certain point I saw evil descend to there. That was in 1989. Since then I returned a few times and I did not see any return of the open holiness,-- yet.