Regardless of any opinions one might have as to the use and application of classification, in the eyes of the US government taking these documents without authorization is harmful by definition.
sorry, it's the future, these are apparently mandatory now.
The defining characteristic of US classified documents is that their release would cause some degree of damage to US national security, ranging from harmful to gravely harmful. here's a Cornell Law writeup that squares with what I know here.
Regardless of any opinions one might have as to the use and application of classification, in the eyes of the US government taking these documents without authorization is harmful by definition.