Changing the diaper in the cabin and in the lounge is absolutely disgusting. Diaper-changing is a private matter that should be conducted privately. Doing it in public, nevermind in the confines of an airplane cabin--regardless of the class--is highly impolite and inconsiderate. I'm certain I would have spoken to a crew member and, if he'd done it more than once, then to proud papa who should have taken his baby's dirty bottom to the toilet.

If the argument runs that children have every much as right to be on airplanes as grown-ups, since they pay the fares the airlines charge, then the children will be held to the same standard--and their guardians will be expected to enforce those standards accordingly. If some passenger decided to defecate in the aisle because it was more convenient than in the loo, you'd probably have a riot followed in short order by a diversion, then one pax freezing his bottom off on a cold landing strip in Kamchatka. I fail to see why the father in this situation (though not the innocent infant, who doesn't know any better) shouldn't suffer the same fate.

Take it to the lav, or leave the baby at home!