Students should be allowed to talk about controversial topics, it is part of the learning process. Students should be able to freely express their views and sides of all types of topics without fear of being ridiculed or punished by an authority figure. It is freedom of speech and expression.
Controversial topics are best discussed with peers in school. They have to learn about the social issues in the world around them, lest they come out ignorant and looking dumb when the issue can't be avoided. Student's should be able to express their freedom of speech, and should be encouraged in class