I think the major objection is career progression i.e. upgrade and dollars. I do see a benefit, I think that if they do raise the age to 67 you could relegate those pilots to the right seat. This would fall right in line with the FAA mandated PPD Program (Professional Pilot Development). The experienced over 65 pilot in the right seat could act as mentor to the newly upgraded Captain, this allows the FOs to get to the money and the upgrade and it also keeps experience in the cockpit. Now if an over 65 pilot doesn't want to take the right with the pay and seniority associated with it, they can retire.