Whether it's the mantra of the left or not, I do not see benefit in doing what this guy did. He probably thought it was harmless and funny - and I think it was - but he has to understand before he clicks send to parents in his school district that not all of them will. In society the way it is today, those kinds of things have and will continue to get people fired because of the perceived polarizing effect they have. It sucks but that's what it is.
When anyone on the right makes a derisive comment about the ONE, or questions his motives, or protests his agenda (or the mosque), there is a call for an investigation or a firing.
The attitude that you have taken in this (I'm not condemning, just making an observation) is precisely the reason why the left gets away with all they do and the right is subjected to insult after insult after insult (often resulting in firings, resignations, prosecutions, etc, etc, etc.). Until WE stand up and say enough the left will continue using this form of censorship against us.