The focus should be on independent critical thinking.  Too much opinion nowadays is based on biased information and logical fallacies.  For example, "Trump's first statement in response to the Charlottesville protests did not mention specific groups such as the KKK, therefore Trump is a White Supremacists, therefore all Republicans are White Supremacists."   On current and historical events, students need to come to their own conclusions, uninfluenced by the bias of a teacher.  I spent 40+ years as an educator and kept my mouth shut on the specifics of politics because that was what was expected of me.  Here's a good online lesson appropriate for high school students. 
 https://owl.english.purdue.edu/owl/resource/659/03/