> I'm a fan of Dennett

Then please don't misrepresent what he's actually saying.

In the video you linked to, for example, he is not saying that your conscious experience of looking at the blue door doesn't exist. He's not saying that your mental state when you perceive the blue door doesn't exist. He's saying that what underlies that conscious experience and that mental state is not some magical "phenomenal quality of blue" in your brain but functional processes in your brain that represent blue (and a host of other concepts) in a functional way. In the video he even calls himself a "functionalist" with respect to "mental properties" like blue--those properties are functional properties, not "phenomenal" properties. But functional properties exist, and so do the conscious experiences and mental states they underlie.

Why does Dennett say that "phenomenal properties" don't exist? Because, to put it as briefly as possible, they're magic. Your mention of Christian apologists among his critics is quite apt, because, to a physicalist like Dennett (and like me), the Christian apologist's view of how minds work in general is magic. Why do you experience blue? Because God endowed you with a magical "mind" and "soul" that experiences blue--blue is a "phenomenal property" of your mind/soul. Whereas Dennett, as a physicalist, spent his career talking to experimentalists in cognitive science who were actually figuring out the physical processes that go on inside brains when people are experiencing blue (or anything else), and explaining them in functional terms.

If you go back to Dennett's earlier work in the late 1960s and 1970s, you find that he actually tried to use terms like "phenomenal qualities" (and "qualia", another term that pops up a lot in his writings) to mean functional properties--i.e., he tried to say something like: yes, "phenomenal qualities" exist, but they're functional properties, they're not magical. But he found that whenever he tried to do this, people would object: they would read his description of what functional properties are and say, No! That's not what "phenomenal properties" and "qualia" are! And they would go on to list properties that, to them, "phenomenal properties" and "qualia" must have--and they were properties that no physical process, no non-magical entity, could possibly have. So eventually Dennett decided that it was pointless to try to convince people to use terms like "phenomenal properties" and "qualia" to mean functional properties--they just wouldn't accept that. And that is what led him to take the line he took in his more recent work, and in the video you referenced, where he just says point blank that "phenomenal properties" and "qualia" don't exist--by which he means what I have just described, that no physical process, no non-magical entity, could possibly have the properties that proponents of "phenomenal properties" and "qualia" insist that those things must have. But that doesn't mean conscious experiences and mental states don't exist; it just means they are "made of" functional properties of brains, not "phenomenal properties" or "qualia".

In short, Dennett decided that the best place for him to draw a line in the sand was not at the meaning of terms like "phenomenal properties" and "qualia"--he found no useful alternative to simply letting proponents of those terms define what they mean and accepting their definitions, however useles he found them. He decided that the place to draw the line in the sand was at the claim that "phenomenal properties" and "qualia" are what underlie our conscious experiences and our mental states: no, he said, that's not what underlies them. Our conscious experiences and our mental states are not magic. What underlies them is functional processes in our brains. Those processes, and the conscious experiences and mental states they underlie, are perfectly real. They just aren't "phenomenal properties" or "qualia" as proponents of those terms insist on defining them.