That's what I thought at first - there's no need to show racist cartoons to students in order to teach about freedom of speech.
But it could have been a mistake, since the teacher apologized. It should never have been blown up.
Is it really about freedom of speech? Which class teaches about freedom of speech?
If it's why would you show a cartoon like that? Like, are you saying it's okay to insults religions but you can't do this against Ethnicity, Sexual Identification, etc???
To whose values is it okay to make fun/ insult other peoples' religion? Is it not common in the world to show respect different cultures?