The vast majority of our Founders hated slavery, even though they owned slaves.
The institution was so entrenched that they could not figure out how to get rid of it in their lifetime.
Most opted to free their slaves upon their deaths.
Thomas Jefferson's Paragraph on Slavery in his original draft of the Declaration of Independence
Very few in the current era would understand, but many of them felt obligated to keep and maintain their slaves because they feared what would happen to them if cast out into the world to fend for themselves. Even though they opposed the institution of slavery, they’d inherited them for the most part and did what they thought was best for them under the circumstances.
But not Thomas Jefferson.