Your claim that "material support included speech in the past" is misleading because it misses the crucial distinction between public discourse and direct assistance. The First Amendment continues to fully protect public advocacy. You can write, speak, and argue publicly in favor of any cause. What the Supreme Court prohibited was not the expression of an idea, but the action of providing a professional service directly to a designated organization, such as giving "expert advice" or "training".

In short, the law distinguishes between expressing an independent opinion (which is legal) and using your speech as an expert tool to help a group operate (which is not).