As is the case with many general observations about free speech jurisprudence, the proper response to your point is "Yes, but...." ;-)
Glen is correct that passing a law requiring that the protest must be held at a distance removed from the service would hold up as Constitutional. The 2-mile threshold might be more than the Court would provide for, but laws requiring such protests to be out of sight of the funeral,
and conducted either before or after the services have withstood court scrutiny, and will continue to, because the Government is allowed to impose "time, place and manner" restrictions on speech in certain conditions, if the court deems the balance of the competing interests in play to weigh in favor of such regulation.
In the recent case that Westboro triumphed in at the Supreme Court, the Phelps clan was sued for intentional infliction of emotional distress (among other claims), but since they had followed local laws when conducting the 'protest' in question, and there was no overt attempt to harm the plaintiff directly (in the eyes of the court, at least), the appellate court's overturning of the original jury verdict in favor of the plaintiff was upheld.
So.... yes; the courts have held what Westboro does to be free speech, but the courts also permit restrictions on how and where they express their vile point of view.
