(I didn't see Nate's post before posting this, which is more response to Don's last post.)
I think a lot of this battle is being fought subconsciously on the issue of the meaning of "truth." I think DeWitt almost surely has to be correct in his assertion that Epicurus did not understand "truth" as an absolute term, but in terms of something being "truly reported" as if by a witness in court, who is reporting without opinion, but who may well not have access to all the facts.
The Academic world, however, including Plato and Aristotle and Stoic derivatives, are fully invested in there being an "absolute" truth which is accessible, if at all, through conceptual reasoning. Therefore they cannot imagine themselves, and cannot tolerate in opposing views, any standard of "truth" which does not include conceptual reasoning as core to the definition of what is true or false.
But that seems to be exactly what Epicurus did, setting "Nature" as the provider of each and every criterion of "truth." At the same time , of course, Epicurus studied and discussed how the mind works with conceptual reasoning, in which opinion is involved. So that's why I think we see Epicurus discussing both conceptual reasoning as well as the set of tools given by nature by which conceptual reasoning must be tested for its accuracy and relevance to us as individuals.
And I guess in saying that we might see another reason for the hostility -- to suggest that the power and relevance of conceptual reasoning should be "tested" or in any way restrained by faculties of nature would be intolerable to the Platonic team. To them, reason and logic are absolutely supreme, and its easy to read into them (especially into the Stoics) the disposition to dispense with the senses and "reality" totally, in favor of what they see as the higher life attainable through the mind only.