Freedom of speech is a great thing, you can speak your mind and be as offensive as you want (within legal reason) without censorship from the government, however, it doesn't necessarily apply to internet forums as moderators have the right to remove or edit any post which is offensive and is likely to take a thread off-topic as a result of the inevitable abuse the offending member will get back.
Freedom of speech also doesn't mean that the other person can not be offended, it doesn't mean that others can't rip you a new one if you're being an idiot and it certainly doesn't mean that you don't have to take responsibility for your actions.