Observed and overheard the following on a flight. A parent with a lap child was seated in the window seat and a passenger in the same row in the aisle seat while the middle seat was empty. Shortly after take off the parent asked the other passenger, who was sprawled out taking up part of the middle seat, to move so that the child could be placed in the middle seat. The aisle seat passenger declined stating to the effect that the empty middle seat was a community/common area and that the parent didn't have the right to sole use of it and should have bought a ticket for the child if it was important for the child to have their own seat. The parent didn't pursue the matter after the response.

What's your thoughts on how the aisle seat passenger handled this?