Correctly attributed to Thomas Merton:
When I criticize a system, they think I criticize them – and that is of course because they fully accept the system and identify themselves with it.
The entire quote is provided in a book – Follow the Ecstasy: The Hermitage Years of Thomas Merton – by John Howard Griffin (p. 97). The larger context is found in a section on January of 1967:
[Griffin:] On January 9, he received a letter from a former nun who hoped to return to her order, scolding him [Merton] because she had read a review in National Catholic Reporter of Raids on the Unspeakable and Conjectures of a Guilty Bystander, and “telling me I was a naughty old world-hater and that the world was really lovely, how everyone really loved everyone else and all was Paradise in Texas.”
Typically, even though Merton dismissed the letter as a naive and narcissistic document, he assumed that he was at fault for this kind of failure to undersand his work.
[The full Merton quote:] “Too loud, too sweeping, too preachy. When I criticize a system, they think I criticize them – and that is of course because they fully accept the system and identify themselves with it. All love and bliss! And they seem to have no idea that the affluence (which for them is the Kingdom of God) has another side to it – the buried bodies of children in Vietnam and the Negro-Puerto Rican ghettos.”
[Griffin:] The monk spoke of such correspondents as “pious souls with their pretty myths about the world.” Only the subject was different: “Instead of sweet Mary and Baby Jesus, it is now sweet sweet world of automation and jets and freeways – and tranquilizers, I guess also.”