> Use the library. Don't write your own.

Things are not so simple.

Dependencies on 3rd party libs also imply maintenance costs (generally related to the integration of this lib into your build system). They are moderate, however, they don't go away with time.

Binary search is a small algorithm, which is easy to understand, and whose correctness is easy to check. It's not a good example of a "good" dependency on a 3rd party lib.