This writing prompt is a basic opinion based writing prompt. There is not a definitive correct answer, so go with what you feel is actually true. A savvy reader can generally "feel" a writer's truth and passion.
Because your writing prompt is an either/or writing prompt, I recommend using a double sided thesis statement. This kind of thesis statement begins with a dependent clause that states the side of the argument that you are not in favor of. That dependent clause is then followed by an independent clause that contains the argument that you are in favor of. An easy way to start this kind of thesis statement is with the word "although." For example, you could use the following thesis statement.
"Although the Bill of Rights states that United States citizens have freedom of speech, the reality is that the freedom of speech is little more than illusion meant to placate citizens."
That statement is easily flipped around to support the opposite.
"Although many people feel that freedom of speech is an illusion, the reality is that each and every citizen is guaranteed that freedom by the Bill of Rights."
This kind of thesis statement is a solid start because it forces the paper to acknowledge and discuss opposing arguments. This generally helps antagonistic readers open up to your main argument. They want their feelings and opinions to be verified, and your thesis statement and body will do that; however, the final half of your paper will show why your main argument is superior.
As for the three points of support, that is up to you. I would definitely spend time looking into the exact specifics of the amendment because it does not guarantee citizens the right to say anything they want whenever and wherever they want to say it.