I know that sounds circular, so I'll expand. We can't know exactly how one person experiences a particular shade of red vs another person. But we can know that one person can experience the exact same shade of red in different ways in different contexts: what thing is red (a rose vs a welt), or what it the current lighting is, or their mood on different days. From that we can conclude that the red qualia isn't some transcendent fixed property.
We also know from experiments on conscious, human subjects undergoing brain surgery that stimulating certain networks can result in complex phenomena: eg, the subject smells fall leaves with a hint of maple syrup, say. Or they suddenly feel the impression of being in the presence of a long dead aunt.
The brain builds up associations, and each "node" that is activated nudges associated nodes into activation, and so on. I assume we've all had the experience where we are trying to remember the name of someone: we picture them in our mind and all we can come up with is the feeling it has two syllables and starts with a vowel. In those cases those associations are manifest but it wasn't enough to trigger the primary node (the name) we are seeking.
Why can't qualia simply be the state of consciousness when a particular set of nodes are in a particular state. So many other experiences seem to be exactly this; why assign a mystical, non-physical property for the case of subjective experiences?
I'm in the camp that the most likely outcome is that artificial neural networks can be conscious and have real experiences, but the toy networks we have today don't have nearly the right topology to achieve such states.