From a March 14 Washington Post live chat with Post associate editor Robert Kaiser (h/t Howard Mortman of extrememortman.com). Portions in bold are my emphasis:
Washington: How is the lobbying system not legalized bribery, and wouldn't ending lobbying by the rich empower the rest of us and revitalize our democracy?
Robert G. Kaiser: How would you end it? Isn't lobbying a form of speech? Isn't speech protected by the First Amendment?
And keep in mind, though many lobbyists do represent rich corporations, there are also many representing labor unions, teachers, non-profits, environmental groups, civil liberties advocates and so on. Even newspapers have lobbyists.