It doesn't matter what you say, I can guarantee that someone, somewhere will be offended. That being said, no, I do not think someone should insult any race or religion, whether they are a member or not.
This is the USA, not Putin's Russia or Assad's Syria. My First Amendment rights guarantee my freedom of speech without the caveat that my words adhere to your standards. That is why it is called "free speech". That being said, being rude is never a nice thing, but I defend my right to choose my own words.