Guarding the flock was given as instructions to the pastors and elders in the First Century.
Jesus warned us to beware of false prophets.
All of the New Testament, with the exception of Philemon, addresses heresy and false teachers.
Apologetics and defense of the faith are biblical, but all of those were part and parcel of church life with accountability.
The call for discernment seems to have birthed a sort of apologetics industrial complex of discernment ministries.
But are they servants of cowboys?