Sisemen, your post is deliberately offensive, and bullsh!t to boot.
It´s not either/or; it´s both. And you know it.
All pax pay. Which entitles
all of them to be treated courteously by us, the airline´s staff.
Similarly, all pax need to treat airline staff and each other with respect.
Part of that is obese pax needing to carefully read their chosen airline´s policy for big pax, and, as the OP in this case, trying to inform themselves about the situation.
Well done
MHM for asking, and well done
girtbar for that perfect answer about your airline´s way of dealing with this matter.
Walter, much more effective than playing the abrasive tough guy on an anonymous internet forum or making a scene on board, is printing out your carrier´s policy on obese pax.
If you find yourself in the very uncomfortable situation of being squeezed by a neighbour overflowing his/her seat, ask for the FA in charge before take-off. Show them their own airline´s policy and politely insist that you expect them to enforce it.
If you, rather than starting off with communicating like a civilised adult, would start off by making a scene instead on a flight where I was in charge of the cabin, I´d not be inclined in any way at all to accommodate you. Never mind the circumstance.
Behave like a Neanderthal on board, and get treated accordingly.
Behave like an abusive Neanderthal and get off-loaded ASAP.
Politely insist on what is right, at a time when the crew can still take effective action, and you will succeed.