I think it is of interest that in most cases,
airlines have a rule about overweight passengers. Jurgens post doesn't get specific about whether or not the passenger he was next to had to use a seatbelt extension and couldn't put the armrest down. In most cases, the passenger who can't fit has to buy a second seat at the time of booking or if they can't be seated they have to book two seats on a later flight.
Airlines that require a passenger to buy a 2nd seat when they can't fit into a seat with the armrest down include
Allegiant
American
Frontier
Southwest advises the customer to discuss their situation at the gate and if there is room available they will accommodate with a complimentary 2nd seat. Sounds good but most of the time when I've flown SW they're flights are full. It's possible they may ask for a volunteer to take a later flight to make room.
Spirit Airlines advises to buy a second seat at booking or book their
United requires that the passenger buy the extra seat for each leg of their journey. They also can buy a first class seat or business class
Notice that in each case the passenger that is overweight that has to be to make the proper booking, not their fellow passengers.
I think a lot of you are also ignoring that it is a safety issue also.
Jurgens was wrong to tweet about it without bringing it up to the flight attendant. The airline was wrong for not accommodating him if they weren't going to have the overweight passenger take a later flight and book two seats or move them elsewhere.