A purely "defense" contractor, protecting the country itself? No, nothing wrong with that.

But what is euphemistically called "defense" is far more often about offense - attacking those countries and people who displease or are inconvenient to you, making sure the world is structure to suit your* interests, usually at the expense of the interests, and often the lives of people elsewhere in the world.

* - In reality, the interests of the elite of your country.