I can't find it, but there was a Nuzlocke Comic which had the characters address this. The scene took place after the player talked with N on the Ferris Wheel and is feeling kind of depressed since N pointed out how we're forcing Pokemon to hurt each other and that reminded the player of the Pokemon they lost. Then Bianca appears and she says she's been helping Juniper (hinting to her eventual role in BW2 which was pretty clever) and Bianca explained that Pokemon allow themselves to be servants because they grow stronger from bonds with trainers, pointing how Wild Pokemon are weaker than trained Pokemon. That scene answered pretty much the question that needed to be answered in BW but was pretty much dropped.
That's exactly what I was hoping somebody would address. So we know that in any other context we would have squads of guys and gals in combat gear dropping down onto the Indigo Plateau and hauling off Lance and company for enslaving creatures and forcing them to knock each other out presumably against their will, and allowing minors to skip their education entirely and pursue training these creatures to knock each other out. Ah, but they like it! There's bonds between trainer and Pokemon! I wonder how that works from the Pokemon's perspective. Since only a few Legendaries are capable of articulating that yes, those bonds do exist, and that yes, these Pokemon actually fight willingly (and most of them through telepathy at that), you can hardly expect the Pokemon to confirm this, and even then one wonders if they truly believe that or have been coached/coerced to say so. So it would be nice if someone, somewhere, can delve into the psychology of this, to perhaps explain just what keeps our beloved pastime above "glorified dogfighting", as so many critics call it. Because I don't know about you, but I don't think what Black and White offered would convince many people.
EDIT AFTER READING THE COMIC: Holy crap, that's beautiful. Vader_the_White, thanks for finding that. That's more or less exactly what I was looking for.