Final answer:
The main idea of Ida Tarbell's work is to expose Rockefeller's aggressive strategies in establishing Standard Oil as a harmful monopoly through detailed investigative journalism.
Step-by-step explanation:
The main idea of the first excerpt from Ida Tarbell's work in McClure Magazine, which discusses Rockefeller's character, is to highlight the predatory and aggressive business practices of John D. Rockefeller's Standard Oil Company. Tarbell's investigative journalism went beyond just reporting; it exposed the unethical methods Standard Oil used to establish and maintain a monopoly. She meticulously researched court filings and internal memos to shed light on the ways Rockefeller's empire was built at the expense of competitors and the public interest.
Unlike her contemporaries who may have engaged in more sensational journalism, Ida Tarbell referred to herself as a historian, using her talent in researching and analyzing primary sources. Her work, The History of the Standard Oil Company, is a seminal example of what would become known as muckraking journalism, albeit a term Tarbell herself did not favor, as it led to significant reforms including the eventual breakup of Standard Oil.