As striking workers circled outside Kaiser Permanente medical centers throughout Northern California on Tuesday, hospital and union leaders traded allegations about the motivations behind the bitter dispute. Much of the controversy centered around the striking nurses, who have a contract through 2014 but walked out in sympathy with mental health and optical workers who are negotiating a new contract. A hospital association ran a full-page newspaper advertisement claiming the nurses have no sympathy for patients and are only concerned about increasing their membership.