The article argues, and I agree, that a university is free to not invite someone if they view them as controversial. Where the problem really is is that they invited him and then retracted the invitation in response to a mob. The retraction is what makes this problematic.
EDIT: the other point that the article makes is that this professor's "controversial" views are held by upwards of 70% of the American public. The net result of applying this rule consistently would be that a strong majority of the American public cannot express their opinions on this subject because of a tiny vocal minority.
EDIT: the other point that the article makes is that this professor's "controversial" views are held by upwards of 70% of the American public. The net result of applying this rule consistently would be that a strong majority of the American public cannot express their opinions on this subject because of a tiny vocal minority.