“Anonymity is a shield from the tyranny of the majority. … It thus exemplifies the purpose behind the Bill of Rights, and of the First Amendment in particular: to protect unpopular individuals from retaliation--and their ideas from suppression--at the hand of an intolerant society. The right to remain anonymous may be abused when it shields fraudulent conduct. But political speech by its nature will sometimes have unpalatable consequences, and, in general, our society accords greater weight to the value of free speech than to the dangers of its misuse.”

"Whodunit? Who Meddled With Our Democracy?" Part 2 http://american-exceptionalism.org/whodunit-who-meddled-with-our-american-democracy/, The Heartland Institute, May 18, 2018.
2010s, 2018

Ashcroft v. Free Speech Coalition, 535 U.S. 234 (2002) (Opinion of the Court).

"Sayings" at Richard Stallman's personal site (c. 2001)
2000s

Citizens United v. Federal Election Commission, 558 U.S. 310 (2010) (Opinion of the Court).

This appears to be a manufactured quote for a PBS documentary on the American Revolution, created by condensing, rewriting, and paraphrasing portions of a lengthy letter James Madison wrote to Thomas Jefferson on 17 October 1788 http://oll.libertyfund.org/?option=com_staticxt&staticfile=show.php%3Ftitle=1937&chapter=118854&layout=html&Itemid=27, about the need for a Bill of Rights and the danger of an establishment of religion. The resulting "quote" profoundly changed the import of what Madison was trying to say and uses modern English. The phrases "biggest danger" and "tyranny of the majority" aren't even in the original letter. The relevant portions of the original letter are (italics in the original; bold added for emphasis):<blockquote>"… In Virginia I have seen the bill of rights violated in every instance where it has been opposed to a popular current. Notwithstanding the explicit provision contained in that instrument for the rights of Conscience, it is well known that a religious establishment would have taken place in that State, if the Legislative majority had found as they expected, a majority of the people in favor of the measure; and I am persuaded that if a majority of the people were now of one sect, the measure would still take place and on narrower ground than was then proposed, notwithstanding the additional obstacle which the law has since created. Wherever the real power in a Government lies, there is the danger of oppression. In our Governments the real power lies in the majority of the Community, and the invasion of private rights is chiefly to be apprehended, not from acts of Government contrary to the sense of its constituents, but from acts in which the Government is the mere instrument of the major number of the Constituents. This is a truth of great importance, but not yet sufficiently attended to; and is probably more strongly impressed on my mind by facts, and reflections suggested by them, than on yours which has contemplated abuses of power issuing from a very different quarter. Wherever there is an interest and power to do wrong, wrong will generally be done, and not less readily by a powerful & interested party than by a powerful and interested prince. …"</blockquote>
Misattributed

As quoted in With Prejudice : The Perspective of an Acquitted Defendent (2010) by Vicky Gallas; no earlier occurence of this phrasing has been located (Relevant quote: "Il n’y a point de plus cruelle tyrannie que celle que l’on exerce à l’ombre des lois et avec les couleurs de la justice" i.e. "There is no tyranny more cruel than that which is exercised within the shade of the law and with the colours of justice." See Chap. XIV of Considérations sur les causes de la grandeur des Romains et de leur décadence).
Disputed

Source: Democracy: The God That Failed (2001), P. 218.

Source: https://books.google.com.pk/books?id=co3AzQEACAAJ&dq=inauthor:%22Zaman+Ali%22&hl=en&sa=X&ved=2ahUKEwjVi-2e57jtAhWToVwKHUj0D3kQ6AEwAnoECAEQAg

Ashcroft v. Free Speech Coalition, 535 U.S. 234 (2002) (Opinion of the Court).