One man helped build the deterrent that held for fifty years. His son spent his life arguing with what it became. The third is trying to build the layer that makes both arguments unnecessary.
Each stop is a page in the graph. The order is an argument — but every one of them is also a door into the rest of it, so you can leave the path wherever it stops being useful.
His father marched to make a system admit people it had excluded. That was the right fight. But a system that can be made to admit people can be made to exclude them again, usually within a generation. The promise was not to win the argument — it was to build the thing that makes the argument unnecessary.