The quote you are referring to refers to Stephen Kinzer’s research monograph Overthrow: America’s Century of Regime Change from Hawaii to Iraq. The specific argument he makes in that book is that the overthrow of an unfavorable dictator, president, or prime minister was not enough; the intervention of the United States proved to be the decisive factor in precipitating a regime change. To begin thinking about how to answer your question—was intervention necessary because of economics or because of America’s modernizing mission—you might want to consider the underlying implications of American involvement in territories overseas.
One of the key arguments Kinzer makes in Overthrow is that US foreign policy was usually based on deceiving an otherwise idealistic American public into believing that it invaded foreign territories with good intentions. However, more often than not, foreign policy makers were indifferent to the welfare of indigenous populations and actually did more to prevent the emergence of stable, self-governing nations. Take, for example, his discussion of the American, CIA-led operations against the Guatemalan leader Arbenz. Kinzler argues that the land-reform programs that Arbenz had launched at the beginning of his presidency directly undermined the profitability of the American company United Fruit in the region. Many American politicians, lawyers, investors, and others in the Eisenhower administration had connections to United Fruit, and they stood to lose money if the company’s contracts with local landowners were threatened. The administration, framing the ouster of Arbenz as an attempt to prevent the spread of Communism in Latin America (Kinzler argues), was really a thinly veiled effort to protect American business interests. This seems to undermine the argument that the US was interested in “modernizing” foreign nations.
On the other hand, Kinzer also provides examples of US foreign interventionism that seemed to justify an American attempt to protect liberal, democratic principles worldwide. The 1983 invasion of Grenada, issued by the Regan administration, was a putative effort to stop a bloodthirsty Marxist regime from assuming power on the island and to protect American medical students who were studying there. Again, this is only Kinzer’s interpretation of the events, but it seems to suggest that the United States could become involved in the politics of other countries for non-economic reasons.
You can defend either choice, it just depends on how you interpret the case studies Kinzer provides in his research.