Is that based on your law degree? The fact that they were taking a fee is what meant in the eyes of the law that they were running a business. You are not legally responsible for what people do with the code you right. You are legally responsible for having the requisite business licensure if you run a business. They did not go to prison for writing code. They went to prison for running an illegal business and it was a business because they were profiting off of people using the service.

If others using your software code alone incurred legal liability then most of the maintainers of pen-testing tools would be doing federal time by now.