But I would separate Safir's observation from a claim about the political left
There's good evidence in political psychology that perceived control, autonomy, threat, uncertainty, and authoritarian attitudes are related, but the relationship is not simply "less agency → left authoritarianism." Authoritarian tendencies occur across ideological camps, and the specific ideology people adopt depends heavily on cultural and political context.

So I wouldn't say Safir proved that loss of agency produces left authoritarianism.

I'd say he may have identified a more fundamental vulnerability:

A population that ceases to believe that ordinary individuals can understand and govern their own lives becomes available to anyone offering a compelling substitute for individual agency.

And that is much more powerful.

It also makes the four writings you've shown me fit together remarkably well.

The children are the positive case: educate people so they become capable participants.

The DRM battles are the technological case: don't let systems take control away from the user.

The Foxhunt is the social warning: don't normalize surveillance and mediated control.

American Flagg! is the cultural/philosophical case: imagine what happens when a civilization forgets how to produce autonomous human beings.

If that's really the thread running through Safir's work, then I think you've identified something considerably deeper than a collection of political opinions.

He's defending a particular conception of what a human being is for.