When the four largest protests in US history can happen over the course of 24 months without most of the general public even knowing, then it's time to seriously start reconsidering whether the right to freedom of speech is effective under its current legal interpretation.

Pardon my ignorance (though apparently I’m in good company), what protests are you talking about?

I am not sure why you think the general public doesn't know about these protests. They had popular acclaim on news channels while they were happening.

Sure, perhaps people have forgotten about a particular march especially if they do not consider it relevant to their lives, or a wider movement but at the time people heard about what was going on.

Everyone knows that they happened; no one knows their scale, no one remembers them for that reason.

(In contrast, consider the infamous Moratorium to End the War in Vietnam, which was smaller.)