> Still, a person who knows what he/she is building can likely predict how it is going to be used. Would I want to be responsible for popularizing portable black hole generators?

You just developed an insanely small part of this machinery. Compartmentalization of the work appeases the mind a lot. :-(

If you still have bad feelings, there exists the charity-industrial complex: donate some decent paycheck to give a poor, starving child a better life - something that you could not have done if you hadn't accepted the well-paid defense contract.