While I hope it's obvious why it isn't fair to treat others as immoral or stupid, it may not be immediately obvious why it isn't always smart to do so. To be sure, sometimes it doesn't matter, but when it comes to war and politics, it often does. For example, in war it's often dangerous to treat your opponent as stupid (as General George Patton clearly knew, which is why he held opponents such as the German General Erwin Rommel in such high esteem).
Unfortunately, this has happened over and over again since 9/11. Islamic terrorists have been repeatedly portrayed as poorly-educated, religious fanatics, who are motivated by visions of heavenly grandeur when in fact most are well-educated (especially when compared to the countries from which they come) and come from secular and middle class backgrounds ("Terrorist Stereotypes and Misconceptions"). John Updike's novel, The Terrorist, somewhat reflects the uninformed perception.
The same is true in politics. While it's tempting to treat one's political opponents as beneath you, it is ill-advised to do so. In the early 2000s, Democrats repeatedly mocked the religiosity and intellect of theologically conservative Republicans. However, as the cognitive scientist and UC Berkeley professor George Lakoff ("Don't Think of an Elephant") who was the darling of the political left during the 2004 Presidential election, warned his liberal colleagues, just because conservatives see the world in a different way, doesn't mean they're mental midgets. To do so, is a mistake:
A lot of progressives hear conservatives talk and do not understand them because they do not have the conservatives' frames. They assume that conservatives are stupid. They are not stupid. They are winning because they are smart. They understand how people think and how people talk. They think! (p. 17, emphasis added).So, what's the takeaway? I think a good operating strategy, regardless of your ideological leanings, is to assume that until proven differently your opponents are smart, moral, and competent. Assume otherwise at your own peril.