Leo Strauss was opposed to historicism. He argued that its development since the Enlightenment was at the base of much what was wrong with modernity. In other words, Strauss argued that there are indeed certain fundamentals and that historicism's focus on the uniqueness of historical periods ignored these fundamentals to society's detriment.
This doesn't make Strauss a "fundamentalist" in any religious sense, or an advocate of orthodoxy. Indeed, he viewed these fundamentals in some ways as impossible to answer questions (e.g., just think of the classic problems which philosophy has faced since its advent). Of course some of these "fundamentals," or the rather immutable aspects of humanity, were indeed "fundamental" in the sense of being notions which were true throughout the ages. His notions on the natural inequality of man is one of these.
Strauss wanted some of these fundamentals hidden, particularly the "fundamental" question of whether we are a special creation or not. It seems that he thought to question this openly amongst non-philosophers was to endanger human society.
While I find the notion of "fundamental questions" to be a fascinating one and one which gets at the crux of a number of issues, I find his outright rejection of historicism to be troubling.
First let us note that Strauss did not reject history as a field of study. Indeed, he found it to be a good way to discover the nature of the "fundamental questions," since history illustrates the difference between the tradition of one culture and other cultures and thus the potential difference between tradition and nature. However, the use of history to justify what one might call historical particularism bothered him.
So what troubles me about Strauss' rejection? Well, it seems to me that up to a point that historicism can be useful as a means to, hmm, "enforce" tolerance. In other words, too much emphasis on "fundamentals" can lead to as much bloodshed as too little focus on it.