Since there are a couple of issues here (and, actually, the second issue may itself possess some duality of perspective), I'll take them separately...

Whether in First, Business or Steerage, the OP's umbrage at a breast feeding says far more about the OP's narrow and unrealistic perspective than it does about the young mother's feeding her infant. Maybe it's the First Class bit...Is breast feeding OK in the back of the bus, but "lese majesty" up front among the tycoons, moguls, nobles and officers of flag rank?

As for diapering....In front or back of the plane, the two elements involved seem to me to differ a bit, one, pee, barely pushing the envelope, while poop does seem to offend against good order and discipline. It's been a long time since I underwent the travails of traveling fatherhood, but were it I changing an infant within the spectrum barely hatched thru about oneish, I'd really not give a tinker's damn about offense to Prince Philip of Tender Sensibilities or Princess Pat the Pretentious, when it comes to a wet diaper (although lap is a venue preferable to tray table, and wise parents always carry a plastic bag to preserve such items for proper disposal).