The power to tax is the power to control -- or destroy. If the government can levy any tax it pleases on various forms of speech, the sense in which speech is "free" eludes me.
Try a thought experiment. Governments commonly lay a tax of about 10% on the sale of books. If you accept the principle that they have the right to do this, where do you draw the line? Would a 15% tax be acceptable? Ninety-five percent? How about a flat fee of $300 per book? If they have the right to levy the tax and to decide its amount, then NOTHING (except their fear of the public response) prevents them from taxing your "free speech" out of existence.
And here's another thought: most people don't protest about guns being licensed by the government -- often with extortionate licensing fees . . . and the ever-present possibility that the license may be revoked or used to identify gun owners for purposes of confiscation. Does the government therefore equally have the right to license churches? Or books, magazines, videos, etc.?
What part of "shall not be abridged" is unclear to you?
Recommended reading: The Most Dangerous Superstition by Larken Rose