[mrchucklepants]

Their job is more than that.

"The National Security Agency/Central Security Service (NSA/CSS) leads the U.S. Government in cryptology that encompasses both signals intelligence (SIGINT) and information assurance (now referred to as cybersecurity) products and services, and enables computer network operations (CNO) in order to gain a decision advantage for the Nation and our allies under all circumstances."

[1] https://www.nsa.gov/about/mission-values/

[xrayzerone]

So...SIGINT and CNO. Exactly as I stated.

[toomuchtodo]

Security assurance isn’t necessarily cyber warfare. To have the high ground is not the same as using it offensively, hence the expectation of defensive posture as part of the NSA’s mission (although admittedly some offensive activities are to be expected, depending on the situation, such as Stuxnet and Iran).