To be fair Tanya, in your OP you were talking about taking your DC on a long train journey, it really isn't the same as long haul travel.
On a train you can get up and move around, walk down to another carriage, stretch your legs, watch the world go by out of the window, you can walk down to the buffet car to get a snack, they can sit on their seat, your seat, you can change seats if others are free, you might have a table to play a game on, all sorts.
On a plane it really isn't the same, for example, the seatbelt sign comes on and you can't get up or even move child from their seat to your lap. On our last longhaul flight the seat belt sign was on for hours at a time due to severe turbulence. I didn't medicate my DC because they are very good flyers but I don't judge those that do, it isn't any of my business.
Also, I don't think most who do medicate do it to please other people, most do it because it is better for them and they feel it is better for their child. I don't think many do it for the sake of the person in the row in front!