A few observations:
1) Why was Kevin Smith, a presumably well-off successful Hollywood director, flying a budget carrier like Southwest in the first place? He could easily afford a first-class ticket on Delta, United, etc., where he's going to be more comfortable with a bigger, wider seat, more leg room and better service.
Maybe he doesn't spend like a drunken Beverly Hills socialite with no concept of saving for retirement?
2) Southwest's policy is that passengers "of size" can purchase the adjacement seat. Again, the presumably wealthy Kevin Smith could easily afford a second seat.
Kevin Smith had purchased an additional seat, his flight plans changed where the second seat could not be given to him.
3) Kevin Smith, nor anyone, has any "right" to fly on Southwest or any other airline. Under FAA rules, the captain has extraordinary authority to remove passengers if they feel safety is an issue, and it's likely this captain believed that Kevin Smith was either not safely secured in his seat or that his size caused discomfort and/or safety issues for the passengers next to him.
This is why Kevin isn't calling for any problems with his rights being violated. He's acting out as a pissed off consumer by attacking SW's reputation. It should also be pointed out Kevin Smith sat in the seat with the arm rests down, suggesting his size wasn't posing a comfort issue for him or other passengers and Kevin is able-bodied enough I'm sure he wasn't posing any safety issues either.
[4) I've been on flights wedged next to passengers "of size" and it's an incredibly uncomfortable experience. I welcome the airline's policy that requires anyone who can't fit into a seat to purchase an additional seat, because at that point they're infringing on my rights as a fellow passenger to the seat I purchased.
The bolded segment here and the point above are in conflict with one another. You have no rights as a fellow passenger, and as the arm-rests were both down Kevin Smith wouldn't pose any safety or comfort risks. Me? Even if he caused both I would gladly suffer them to sit next to Kevin Smith.