Early in his career and even during his presidency, John Q. Adams didn't express much of a view on the issue of slavery, other than he felt it shouldn't be allowed in the new states of the union.
This isn't surprising for a man of his times, since being in the Northeast, he probably didn't feel it had much of a direct effect on him and he wasn't a direct witness to its horrors. He, like many of his contemporaries felt that abolitionists were radical and even seditious, since they were pushing the fragile United States ever closer towards open Civil War.
However, late in his life he had a change of heart. As a lawyer, he represented the escaped slaves from a Spanish Slave ship in the Supreme Court case United States vs. The Amistad Africans and won their freedom by arguing that although the United States allowed internal slavery, it had joined other countries in preventing the international slave trade.
He also defied the infamous Congressional gag order that the Southern congressional delegation had put in place before the Civil War prohibiting the discussion or legislation regarding slavery in Congress. My favorite example of this is when he continuously would propose to introduce petitions on slavery from current and former slaves in the Southern States forcing the Speaker to shout him down and prevent the democratic process. This united Northern abolitionists and even Southern libertarians against the gag order in particular and the pro slave delegation in general.
John Quincy Adams views on slavery and race were complicated and changed over time, but he certainly was more enlightened on the subject than most of his contemporaries.