Because sometimes AOG we're wrong, history shows us what this blind form of patriotism brings us, the Zulu war and the second Anglo Boer war we're opposed by large swathes of the British people only to be attacked by angry crowds, the unfortunate appearance of facts served to do little by the way of tempering them.
The Suffragist movement was viewed as damned unpatriotic by some, the removal of the right to rule by the aristocracy was viewed likewise by some.
Martin Luther King spoke out passionately against the Vietnam war, American foreign and domestic policy also was he not a patriot?