One can argue the technicalities of the word scab all day. The landscape has changed completely in RLA regulated industries to one that has essentially eliminated the strike as a tool and thus has eliminated the traditional scab in those industries.
Maybe it's time to redefine it as one who crosses a picket line to perform struck work or in RLA regulated industries, performs extra or voluntary work after a contract amendable date (or something to that effect).
It's time to get with the times. Some of our cards have been taken. There's no point in arguing which ones they were.