To write or speak is to (attempt to) externalize one's thoughts. (Dennett does it very well. I'm not criticizing him on those grounds.) But to externalize one's thoughts is first of all to acknowledge that one has thoughts and secondly to act as if (a) one believes that others too are capable of thought and (b) one is attempting to have arise in those others something like the thoughts in oneself that one took the trouble to externalize—to act as if one is attempting to communicate one's thoughts.
But a thought is a subjective experience. So the simple act of engaging in thought externalization and communication is to acknowledge a belief in the existence of subjective experience (e.g., thought) in oneself and others. So it seems absurd to me for anyone—at least anyone who has subjective experience as I'm assuming Dennett does—to write or talk about the non-existence of thought or more generally of the non-existence of subjective experience in general.
The passage quoted below had Dennett denying qualia rather than subjective experience in general. But as far as I'm concerned qualia means subjective experience. Since thought is subjective experience, to deny qualia is to deny thought. Here are two definitions of qualia.
- a property as it is experienced [emphasis added] as distinct from any source it might have in a physical object —Merriam-Webster (definition 2)
- the intrinsic phenomenal features of subjective consciousness, or sense data. Thus, qualia include what it is like to see green grass, to taste salt, to hear birds sing, to have a headache, to feel pain, etc. —A Dictionary of Philosophical Terms and Names