I don't particularly care if riding dragons is in or not, but I defiately don't think it devalues or demeans them. Put it this way - do you think it's demeaning for a pilot to fly passengers somewhere? No? Because he gets paid. If the dragon got paid in some way (perhaps in some form of exotic food or other item), or did so as you had a close relationship with it, I don't see a problem with it. They may be all-powerful beasts, but that doesn't mean they'd necessarily refuse to take you somewhere. In fact they may think it demeans you, as they'll see that you are inferior to them, much like a human carrying a kitten.
There's a bit of a difference here as the pilot doesn't carry you on his shoulders, he pilots a vehicle that you ride on, so rather than the pilot putting himself in the role of a horse, his role is more like that of the driver of a carriage, whereas if dragons let you ride them they'd be like horses, very large, scaly flying and intelligent horses mind you, but horses onetheless.
And the comparison to a human carrying a kitten isn't really accurate as humans aren't told by kittens to carry them, in fact, humans can carry kittens whether they want it or not, whereas in the case of dragon riding, what people who ask for it usually want is probably more along the lines of riding a horse, you mount the dragon when you wish, and control where it goes, and get off when you want, thus the dragon is following your will. This doesn't mean the dragon is doing so unwillingly, after all, you wouldn't want to ride on the back of a flying creature high above the ground if said creature does not want you there, seeing as it could drop you if it wished, the question is, would dragons be willing to do that? The kitten anology only really applies if it's dragons picking you up whether you want it or not, which would most likely be done so they can do to you what the one in the demo did to the giant, not because they want to help you travel more quickly.
Alduin is the Big Bad, and so are dragons. We probably won't find any dragons willing to become taxi's any time soon.
While the dragons as a whole are enemies, it has been implied that we may encounter dragons that are not your enemies, but without knowing what the relationship those dragons will have with the player, if any, it's not relevant to the discussion. Just because they don't want you dead doesn't mean they're willing to let you ride them, or that they'll help you at all, so the implication that not all dragons are hostile still doesn't mean we'll be able to ride them.