Prime example of a situation where if the OP had such an opportunity nothing would be wrong, but since it's not the OP it's not fair.

If I got a whole row to myself would I tap the person infront of me and let that person know? probably not. As others have said it's the luck of the draw. Sometimes I get an open middle, sometimes I get packed in. It's all fair in the long run. To guarantee yourself space you'd want to buy the seats or pay for a higher class.