Can one become too agnostic? I think the answer is yes. This is the sense I get from reading Stephen Batchleor’s book, Buddhism Without Beliefs.
First of all, it is important to lay out a few facts. The Buddha, himself, was hardly an agnostic, nor was he a skeptic. The Buddha was regarded as a "knower of all" (P., sabba vidû), a "knower of worlds", and a "knower of the path". He knew the beyond that transcended the material plane including birth and death. Also, the Buddha is described as one who "knowing, knows and seeing, sees having become sight and knowledge" (M.i.111).
Switching gears, who is to be mainly credited with giving wings to our modern notion of agnosticism has to go to Thomas Huxley (1825–1895). For Huxley agnosticism meant, "Sit down before the fact as a little child, be prepared to give up every preconceived notion, follow humbly wherever and to whatever abysses nature leads, or you shall learn nothing." In truth, Huxley's agnosticism was the guiding principle of the seeker who wished to know but did not know now.
In light of Huxley's understanding of what it is to be an agnostic, we can say that as a Bodhisattva, the Buddha was like Huxley's little child. However, after the Buddha's enlightenment he was no longer an agnostic by any measure.
The above is quite different from Stephen Batchelor's understanding of agnosticism who understands that agnosticism "is founded on a passionate recognition that I do not know.”
To recognize, passionately, that I do not know even steers away from Huxley's little child who may one day know. Batchelor's idea—let’s be honest—is heading towards dogmatic agnosticism. In other words, we cannot know.
In light of the previous, any trace or hint of dogmatic agnosticism is indefensible and contradictory. In plain words, to know that we cannot know we would have to thoroughly know the unknown. But this is contradictory.