Who defines hate speech? Mobs? Who gets to enforce the official definition of intolerant behavior? Trump? Hillary? (hyperbole to make a point) If we don't maintain freedom of speech above tolerance, then we cannot speak out when our words violate the accepted (and as you pointed out, transitory and unpredictable) definition of 'what is fine'.
Do you really want to just stop talking, without recourse, when a future mob decides your words are unacceptable?