The problem with the statements by Warburton is manifold and goes further than responding merely to him. It would be possible to begin by arguing that it is not an appropriate relationship to any philosopher to "trust" them. That is, that trust involves a relation in which one responds to the integrity of someone and perhaps questions of integrity should not be at the forefront of responding to a philosopher. After all, there is nothing about moral qualities that determines the interest of thought one way or the other. This might be thought too sweeping though since surely there are some cases where one might say that revelation of some sort of moral defect prohibited serious consideration? The classic example would be Heidegger's relationship to the Nazi Party but then shouldn't we include the anti-semitism of Frege as well in such evaluations? This kind of point effectively seems to get us nowhere when considering the worthiness or otherwise of contributions to philosophy.
The second question concerns the appeal to the verdict of "intelligent people" whoever they might be. Presumably what is meant here is the notion of the "intelligent public" being people of a certain standard of education, who, despite perhaps knowing little or no philosophy, could hear something and have a basis for evaluating its importance. It's odd that this kind of standard should be invoked at all with regard to philosophy. After all, could the Principia Mathematica meet it? Is it plausible to claim that Book Zeta of Aristotle's Metaphysics could really fit it? Or that the Critique of Pure Reason which Kant declares "could never be popular" could be held to such a standard? All these works involve a technical vocabulary that has to be learnt to read them and require serious study over a long period to really be responded to with any seriousness. Nor are they alone in this as who, after all, could even claim to have got the real point of John Locke's Essay Concerning Human Understanding without a lengthy period of reading?
Why, given that the evidence of need for continuous and dedicated study for philosophical works to be responded to, is there even the pretense that ones of any quality could easily be retailed to a general (albeit "intelligent") public? The reason appears to reside in the citation from Searle that Warburton gives, the impression that there is some form of clarity that philosophy needs to aspire to and which can be held as a test for "good" philosophy. What this clarity consists in and how it is to be measured are rarely, if ever, themselves articulated. The citation of Searle reminds some of us of one notorious occasion in which the quest for "clarity" was itself exposed to some very detailed and difficult questions, the occasion of the "debate" (if such it really was) between Searle and Derrida. The original spark of this was Derrida's piece "Signature Event Context", part of which included a response to J.L. Austin and concerned, indeed, questions about the conditions of communication. John Searle's response to this piece suggested a series of failures on Derrida's part to understand J.L. Austin and, in return, in Limited Inc Derrida demonstrates in serious detail all the ways in which his original article had been misrepresented by Searle. This dispute is one of the sources of Searle's more emphatic commitment to a "clarity" that he had apparently defended in a dispute in which he failed to show the standards of clarity that he was the the titular defender of.
Calls for clarity in philosophy are in themselves obscure since underneath them is a view of what such clarity has to consist in. It must involve the ability to translate thought into a general common medium whose own conditions of possibility are never made transparent. There is evaluation here that does not speak its own name and which can be traced back, in Anglo-Saxon countries, to an implicit approval of a standard of "common sense" that has its own institutional and historical conditions, conditions that the advocates of such a standard of intelligibility have no interest in making apparent. Only under the condition that such conditions can themselves be made stakes of a debate would be it possible to address the question of whether some philosophers are, or are not, more "obscure" than others.