Would you stand by and let people lie about or insult your faith?
It happens all the time. If I responded to EVERYTHING, I'd be playing full-time defense...and would fail to balance that out with proclaiming the Gospel (offense).
Certainly, Jesus' brother, Jude wrote: I urge you to contend for the faith that was once for all entrusted to God’s holy people (Jude v. 3)
But contending for the faith and escalating the antagonism are two different things.