As an unapologetic proponent of Natural Rights which includes the inherent right to Freedom of Speech, it may be a surprise to learn that this is not a 100% Freedom in all situations, it does in fact have limits. But where and when those limits occur must and can only be finite and very limited themselves, and are only on location and not context.
Recently in California 10 students were found guilty of "disruptive speech" (from Foxnews.com), when they attempted to speak over the Israeli Ambassador to the United States while speaking at California University. The charge and court decision here are correct in this case. The main reason why these students did not have protected speech is the forum. Even though the Ambassadors speech was open to the public, the speech itself was not in the public domain, rather a controlled area or setting. This distinction is where the line of Freedom of speech ends, the Public Domain and NOT the Public Domain.
The Public forum is where Freedom of Speech is and ought to be absolute, the town square, parades, assemblies outside or around government facilities, the press or other writings, this is the public forum. What is not the public forum is privately controlled or reserved for another purpose, such as your house, your yard, a sports stadium, or another facility that distinctly separates it from the open public, such as a lecture room at a college. It does not matter who owns the property, it CAN be government owned but still not be in the public domain, meaning freedom of speech can be limited.