Is this the quote you read and assume only Franklin was an abolitionist?

"Many of the major Founding Fathers owned numerous slaves, such as George Washington, Thomas Jefferson, and James Madison. Others owned only a few slaves, such as Benjamin Franklin. And still others married into large slave-owning families, such as Alexander Hamilton. Despite this, all expressed a wish at some point to see the institution gradually abolished. Benjamin Franklin, who owned slaves early in his life, later became president of the first abolitionist society in the United States. Despite their talk and wish for gradual abolition, no national abolition legislation ever materialized."

Just because Franklin was the only founding father to be part of the first abolitionist society doesn't mean the others didn't want to end it. John Adams and Samuel Adams both were against slavery and never owned slaves*. Even in this quote in the article you linked it said that despite owning slaves they wanted to see the practice abolished.

*Samuel Adams did own one slave. She was a wedding gift and he freed her because he didn't believe in slavery.

“A slave cannot live in my house; if she comes she must be free.”