Much of what I’m going to say is said better in the sources I cited throughout my essay, but I can condense things a bit for you. The welfare state argument comes up quite substantial difficulties. I’ll respond to those as well as your claims about behavior and agency.

1. The causal chain (receipt of welfare discourages people from working, therefore people became lazy and unemployment/other undesirable behaviors rose) requires quite a substantial amount of evidence that simply does not exist. For example, we can take as a counterfactual other countries in the world with far larger welfare states than we have in the US. For the US to reach lower-bound Nordic levels of welfare state spending, we would have to spend an additional $1.5 trillion a year. And yet the Nordics do not have disastrously high unemployment or low workforce participation rates. They’re pretty on par with the US in those respects. They also have vastly less poverty than we do. So why would the rather stingy, bargain-basement welfare state we built in the US be able to cause such destruction while a vastly more generous one seems to have no such ill effect? If we’re to say that the particular design War on Poverty programs is to blame here, then the answer is not to abolish welfare but to design it more in line with the Nordics.
2. This evidentiary burden is even higher since we have extremely well-documented reasons to believe that things other than the welfare state were the cause for the rise in Black unemployment and crime in the second half of the 20th century. I linked in particular to this article about how these phenomena resulted in mass incarceration, but their work relies on the evidence gathered by scholars like William Julius Wilson and Thomas Sugrue. If you want to read a book-length treatment of the “alternative explanation” (for really, it’s the welfare state claim that is the “alternative” to the far more plausible explanation here) I can heartily recommend Sugrue’s The Origins of the Urban Crisis. I would sum up the macro-level story this way: sharecropping collapsed in the South both causing and caused by the migration of a lot of Black folks to urban areas, which were ultimately unable to absorb the influx of labor and where deindustrialization also snatched away much of what employment was available, leaving many people in hollowed-out neighborhoods with no resources and no employment. It’s not simply a straightforward story of intentional discriminatory racism, although much of that did happen and the particular shape this history took is impossible without American racial hierarchy. But the fact is, this story is backed up by simply mountains of evidence. We know a lot about this period of history, and for the welfare story to be plausible, it has to come up with evidence that welfare not only has the effects that people like Sowell say it has, but that these effects also wash out the factors I just outlined.
3. On agency and behavior—I think your point here is confused. Behavior, in the way I was talking about it, is just a set of individual things a person chooses to do, but they’re not the sum total of human activity. Of course everyone can change their behavior, but that’s not my argument. Behavior is 1) certainly constrained (but not determined) by one’s social environment, and 2) is not the only thing that affects a person’s destiny: our behaviors do not automatically result in poverty or wealth. Particular behaviors result in better or worse economic outcomes depending on the economic environment they take place in. If you were hard working but you were enslaved, it literally didn’t matter how hard you worked. You were never going to become rich. Likewise, under capitalism with no welfare state, every able bodied person of working age could work and every worker could work very hard but there would still be poverty. And individual behavior is far from the only thing human beings can control! Human beings design economic and political systems, and those systems act back on human beings. Individual agency is real, but it’s not infinite. That is why many people, particularly Black people in American history, have taken hold of their agency by agitating for changing the way things are: abolishing slavery and Jim Crow, fighting for dignified working conditions, pressing for an economy that works for everyone. These are things that people have the ability to do. To pretend like the economic system we have now is somehow the natural reward and punishment for individual behavior is itself to hide human agency. It is human beings who designed that economic system and human beings can fight for different ones.