Is it "rude" to disagree about religious beliefs?

How would you define the difference between legitimate discussion/debate and "rudeness"?
Update: So... rudeness entails:

Personal attacks
Failure to acknowledge other perspectives
Update 2: Swearing or name calling
Update 3: Threatening others with "hell" or violence
Update 4: Trying to "force" others to agree with you
Update 5: Insulting
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