Because I am going to quote, with approval, Antonin Scalia:
There are laws against threats and intimidation; and harsh criticism, short of unlawful action, is a price our people have traditionally been willing to pay for self-governance. Requiring people to stand up in public for their political acts fosters civic courage, without which democracy is doomed. For my part, I do not look forward to a society which, thanks to the Supreme Court, campaigns anonymously (McIntyre) and even exercises the direct democracy of initiative and referendum hidden from public scrutiny and protected from the accountability of criticism. This does not resemble the Home of the Brave.