Designers with impact on evil side

The other day, I was talking to my friend who recently graduated from design school.
He mentioned, "What about the designers who creates guns, bombs, or even tanks? Are they responsible for their designs?"
I struggled. For the purpose of killing others, I can't say it isn't their responsibility however they only designed it. isn't it?
Design for good or evil-- that is really inbetween designer's morality and responsibility, I think.