Ah, Bert, tough issue. I've been an FP for 35 years, 26 in the same town, in solo practice (a.k.a. "a dying breed") and have always struggled with this as well. As always, you have eloquently described the dilemma.
What to do about patients I've known for decades who have those 120 day bills? I have my staff put all the overdue bills on my desk to review. I look through them and we talk it over but how can I discharge a patient over a bill? Every once in a while they will talk me into it, if the patient has been very irresponsible and it seems that to let them get away with not paying the bill will encourage more irresponsible behavior. My collections aren't that great as a result. I suppose if Carl Icahn were my boss, he would fire me in a heartbeat, but I sleep well at night.
I guess I am out of touch, but still think this is a vocation not a job. I know there are other perfectly valid opinions and approaches to this issue, but thought I'd give you my feedback before I trundle off to bed.