That would, of course, break the WGA. The WGA's existence depends on major movie studios needing them. If the movie studios decide to adapt in a way that the WGA is unnecessary... they're dead, and no writer will stick with them, everyone will scab. The WGA would have to beg SAG-AFTRA and the DGA to strike on their behalf, but that would cause... lawsuits; lots of lawsuits; because is it legal for one union to strike to save another union?
Turns out people like watching things written by the best writers - and plenty of studios would defect if they got to be the only studio with access to most of the best television writers in the West.
Someone unaffiliated with the WGA takes a job and then is ostracized? That sounds pretty evil, and it puts me firmly on the side of Hollywood.
The world is different now. Economy is global, people are trying to make a living doing something that makes them happy. Not everyone is a union member, and it’s absolutely ridiculous to extort a young professional from taking a career defining opportunity because a certain, very entitled group decides they want it even better.
Unions striking is within their right. Go for it. But it’s absolutely unacceptable to start blacklisting non-union people who don’t fall in line because the union doesn’t happen to have as much bargaining power as they would have liked.