Regarding chalking things down to "personal choice," the pool of scientists is large enough and the pool of permanent staff positions small enough that there will always be scientists willing to make the "personal choice" to do weapons research. That's the thing about "personal choices," someone somewhere, under the right conditions will make the "personal choice" to do something. If you want people to stop making bad "personal choices," change the underlying situation or the politics.

Societies and the world do not run on personal choices. Sometimes personal choices matter and can have reverberations throughout society, but assuming society can function on an accumulation of personal choices is a child's way of viewing the world. If you want to change something you find disagreeable, influence policy makers or somehow figure out how to change the academic landscape in America (which probably means you again need to influence policy makers). Otherwise, you'll keep finding more scientists making the "personal choice" to develop weapons for uncle sam.