I am all for it. If you cant fit in one seat you should have to buy two. Why make the person next to you uncomfortable because someone can't lower their armrests?
How about if the person next to you smells like a stinkhole? Or uses heavy amounts of perfume? Or has a really bad cold and is sneezing all over my drink? Or has an annoying habit of humming God Save the Queen? Why should I have to put up with that? Are you going to make the person buy two seats because you don't want to sit beside someone that smells like toxic waste?
I happen to be overweight, but the reason I can't put the armrest down is not because of my weight, it's because it happens to hit my artificial hip and is extremely uncomfortable. That hip is going to be in the same place whether I weigh 150 or 350. So tell me how that is fair? By definition, I fit that description, but if it weren't for my artificial hip I would have no problem. There are a myriad of reasons why someone might just fall into this category. And if the person that is complaining happens to be some whiny bitch, well then you are going to tell me I have to pay double? Because "Precious" has a personal space issue?
Try riding the NYC subway at peak time, you'll learn to get over personal space issues in a hurry.
I understand what they are trying to do, to provide the best service for ALL of their customers. But just remember one thing. This is how smoking bans got started. It's not that different. Let's change a few words from a quote from the SW website that Clint put up.
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Why ask smoking Customers to not smoke?
We could no longer ignore complaints from Customers who traveled without full access to clean air due to encroachment by a large amount of smoke whose body extended into the neighboring airspace. These Customers had uncomfortable (and sometimes painful) travel experiences, and it is our responsibility to seek resolution to prevent this problem.