The above is perfectly consistent with my thesis, which is simply that a major theme of 20th-century social movements was the belief that you can change individual behavior pretty much however you want by changing the society that people live in.

I feel like I'm explaining this poorly. You can't make arbitrary changes to behavior under the Marxist worldview by making social reforms. You can get people to further the interests of their social class more effectively by changing their perception of class, or get them to further the interests of other social classes by making them aware of common social goals, but to a Marxist this follows preexisting and fairly strict principles of how people relate to the class structure. To an orthodox Marxist, for example, improving social conditions by means of placing constraints on the behavior of socially dominant classes would be doomed to failure without a corresponding increase in the power of socially subordinate classes: other forms of exploitation would be found, and class relations would regress to the mean.

It's not that you can do whatever you want by hacking society in a certain way; it's that people's psychology is organized in such a way as to lead to more equitable outcomes if you hack society in particular ways. And even describing this as "hacking" is a little misleading; Marx didn't see any of it as a social project, more as the inevitable result of existing social forces. (Incidentally, this is a main point of divergence between orthodox Marxism and Leninism or Maoism, both of which aimed to produce Marxist revolutions "early".)