It does seem rude to me but I don't think I can articulate why. It feels like using your status as a couple to manipulate the likelihood of getting more space which increases the chance of a single traveler having to sit between strangers.
Realistically, the odds of a couple having to sit apart are low; almost always someone will be willing to swap out from being seated in the middle if they can. So the move gives couples an advantage that single people don't have in getting a favourable seating situation. That is why I never do this when traveling with my husband.
Could you please explain? Wouldn't timing of your booking plays a bigger factor - if the couple booked last minute it's likely they'd have to sit apart in various middle seats as well, no? and if you booked before the couple, you could choose either aisle or window?
I think what Miss Unleaded is getting at is this:
- Most people would rather sit next to someone they know (i.e., their partner) than sit next to a stranger.
- Most people would rather sit next to one stranger (i.e., aisle seat, window seat, or middle seat next to someone they know) than sit between two strangers.
- Most people would like best of all to have an empty seat next to them, thus giving them extra room.
A couple booking early enough that there are full rows available is guaranteed to avoid the worst-case scenario of being stuck between two strangers--if they book side-by-side seats, one will be against either the window or aisle and the other will be in the middle between their partner and a stranger (or an empty seat, but that's unlikely unless the plane is empty enough for all the rows to have two people or fewer). If the couple chooses an aisle and window seat, they increase the likelihood of having the undesirable middle seat remain empty, at the risk of ending up with a stranger sitting between them. However, because the middle seat between two strangers is undesirable, if it is booked, they will probably be able to trade back to the side-by-side seats they initially passed up. IOW, the couple uses the fact that they are traveling together to increase their odds of having an empty seat between them while taking only a very small risk of ending up in a worse seating situation than if they chose side-by-side seats. OTOH, if they're successful in keeping that middle seat empty, they ensure that another passenger must
sit between two strangers rather than an aisle/window seat next to one stranger--i.e., their actions have directly worsened the seating situation for that other passenger stuck in the middle.
YMMV whether you think this is just life or whether you think it's unfair gaming of the system, but I think that's what Miss Unleaded is getting at. I personally would choose not to use this trick for the same reason.