Straus to Voegelin:
May I ask you [Voegelin] to let me know sometime what you think of Mr. Popper. He gave a lecture here [at the New School for Social Research], on the task of social philosophy, that was beneath contempt: it was the most washed-out, lifeless positivism trying to whistle in the dark, linked to a complete inability to think "rationally," although it passed itself off as "rationalism" -- it was very bad. I cannot imagine that such a man ever wrote something worthwhile reading, and yet it appears to be a professional duty to become familiar with his productions.
Voegelin to Strauss:
You are quite right to say that it is a vocational duty to make ourselves familiar with the ideas of such a work when they lie in our field; I would hold out against this duty the other vocational duty, not to write and to publish such a work. In that Popper violated this elementary vocational duty and stole several hours of my lifetime, which I devoted in fulfilling my vocational duty, I feel completely justified in saying without reservation that this book is impudent, dilettantish cr*p.