In addition to the information above, William Randolph Hearst, newspaper magnate and yellow journalist extraordinaire, had widely published reports of the atrocities against the Cuban people at the hands of the Spanish. While the reports were exaggerated, they were more or less true, and a moral outcry that began in the churches of the northeast and among socialists and progressives put some populist pressure on McKinley to send a message to Spain, or take some action that would suggest America would not stand idly by no matter what Spain did.
McKinley's primary motivation was, as stated above, to protect Americans and their business interests in Cuba, but there was a public political motivation and benefit for him as well.
In the 1890s, Cuban rebels were fighting against the Spaniards who ruled the island. The fighting eventually led to riots in the city of Havana in 1898. McKinley worried that these riots might lead to the destruction of property owned by Americans or even to the death of American citizens. He was especially concerned about this because many of the Cubans who supported the Spanish were upset with the United States for supporting the rebels. In order to protect the US citizens and their property, McKinley dispatched the Maine to Havana.
This was out of consideration for reducing damage to U.S. citizens and also for the protection of American citizens.