However, we need to understand that constitutionally protected speech is not all encompassing. Anytime speech can cause harm to people and/or property, it is no longer protected. Citing a classic example, you can't yell fire in a crowd theater because the resulting stampede could cause bodily harm. Sedition, or the written or verbal advocacy of a revolt or the overthrow of any authority or government, is punishable under federal law. Calling in a bomb threat, even if false, is a felony punishable by fines and imprisonment. Defamation (libel or slander) is also legally subject to civil lawsuits in all 50 states.
In my opinion, the law that applies to Pam Gellar and her organized event and which overrides her right to freedom of speech is "Inciting a Riot". Here is the definition from the website USLegal.com:
Under federal law, a riot is a public disturbance involving an act of violence by one or more persons assembled in a group of at least three people. Inciting a riot applies to a person who organizes, encourages, or participates in a riot. It can apply to one who urges or instigates others to riot. According to 18 USCS § 2102 "to incite a riot", or "to organize, promote, encourage, participate in, or carry on a riot", includes, but is not limited to, urging or instigating other persons to riot, but shall not be deemed to mean the mere oral or written (1) advocacy of ideas or (2) expression of belief, not involving advocacy of any act or acts of violence or assertion of the rightness of, or the right to commit, any such act or acts.”Technically, the two shooters were not part of the assembled group at the event, but the courts might rule otherwise because their intent was to join the group with the intent to commit murder and violence.
Pam Gellar knew full well that she would most likely incite violence, otherwise, she wouldn't have contracted such heavy security. All those people at "Draw Muhammad" are fortunate that there weren't more shooters and more deaths that day.
Watch: FNC's MacCallum, Pamela Geller Battle over Freedom Of Speech: http://www.breitbart.com/video/2015/05/05/watch-fncs-maccallum-pamela-geller-battle-over-free-speech/
Shouting fire in a crowded theater: http://en.wikipedia.org/wiki/Shouting_fire_in_a_crowded_theater
Westboro Baptist Church: http://en.wikipedia.org/wiki/Westboro_Baptist_Church
Inciting a Riot Law and Legal Definition: http://definitions.uslegal.com/i/incite-a-riot/
Bomb Threat: http://en.wikipedia.org/wiki/Bomb_threat
Sedition: Legal Definition: http://legal-dictionary.thefreedictionary.com/sedition
Defamation Law Made Simple: http://www.nolo.com/legal-encyclopedia/defamation-law-made-simple-29718.html
Boosted Security Prevent Higher Body Counts at Garland Shooting: http://www.thedailybeast.com/articles/2015/05/04/boosted-security-prevents-higher-body-count-at-draw-muhammad-shooting.html