Why is it bad for an assertion to be inconsistent with the evidence? A natural answer is: because then it is false. That answer assumes that evidence consists only of true propositions. For if an untrue proposition, p, is evidence, the proposition that p is untrue is true but inconsistent with the evidence.
That's an answer, but it seems there is an equally promising answer that does not assume that evidence consists only of true propositions. Someone might think that:
JE: If S's belief that p is justified, p is part of S's evidence.
R: If S's belief that p is justified, the processes that produced S's belief were reliable.
Whatever is justifiably believed is a part of our evidence and whatever is justifiably believed is likely to be true. This is because whatever is justifiably believed is the result of a reliable method of belief formation. Thus, if an assertion is inconsistent with the evidence, it is likely to be false. In a conversational context where one speaker asserts p and then both speakers discover that p is incompatible with what is justifiably believed by the other speaker, it is natural to retract p until additional reasons for believing p or for discounting the justification that supports believing ~p. We can explain why it is bad for an assertion to be inconsistent with the evidence without having to assume EST.
Adequate response? I want Williamson to be right, but I can't see what's wrong with this response.