Sounds like the passenger was definitely more wrong than the Southwest agent in my opinion. Publicly humiliating a Southwest employee because they would not break the rules for you is a big
and I have a difficult time faulting Southwest for taking action against such a customer. The biggest fault I have with WN is that they gave him the option of deleting his tweet and flying on them, they should have just refunded his tickets and told him that his behavior was not acceptable.
Edited to add: I would like to clarify that I think the passenger's behavior was over the line because he specifically named the employee, if he had not done that my answer would be different (i.e., if the tweet simply excluded the first name and last initial of the agent).