“Fellow-citizens! there is no matter in respect to which, the people of the North have allowed themselves to be so ruinously imposed upon, as that of the pro-slavery character of the Constitution. In that instrument I hold there is neither warrant, license, nor sanction of the hateful thing; but, interpreted as it ought to be interpreted, the Constitution is a GLORIOUS LIBERTY DOCUMENT. Read its preamble, consider its purposes. Is slavery among them? Is it at the gateway? or is it in the temple? It is neither.” — Frederick Douglass
I’d say calling the Constitution a “glorious liberty document” suggests he found it inspirational.
Of course the abolitionists fought the fight. Are you arguing the Benjamin Franklin was not among them, or that he was not a founder?
Which autobiography did you read? I read all three.