I also have no trouble at all imagining that a robot trained by a naive Bayes classifier (rather than by a kindergarden teacher named Mrs. Weiskopf), could easily recognize those red things as 'red', the piercing thing as 'painful', and the lemon thing as 'sour'. Yet people keep suggesting that robots can't have qualia.

Agreed. As you illustrate here, a lot of talk about "qualia" and "subjective experiences" can easily be interpreted as everyday talk about perception and discrimination between different real things out there in the physical world (e.g. there really is something about the chemistry which we are discriminating when we notice how the lemon tastes, which a robot could, if he has the right sensors, just as easily discriminate), and furthermore I think that this everyday interpretation is the main part of what makes such talk seem obviously true. That is, the philosophical talk about qualia is powered by ambiguity about what is being said, by equivocation between the everyday meaning and the "philosophical" meaning.

Equivocation - saying one thing which is accepted as true, then silently shifting its meaning in order to draw a false conclusion - is a huge problem in philosophical discussion, and it's hard to deal with precisely because the meaning shifts are not easy to notice, since the words remain the same.