The freedoms of assembly and speech are guaranteed by the first amendment of the Constitution. And what are corporations (or unions for that matter) if not groups of individuals assembled for a common purpose? So I guess the left is okay with the freedom of assembly and freedom of speech...just not both at the same time.
Not to mention the fact that if only individuals have free speech...then only those that can afford to personally fund a campaign commercial (i.e. the very rich) will be allowed to do so.