Your belief is based on largely the same bankrupt propaganda as what the progressives push.
The automatic assumption on part of progressives is that a slave owner is automatically destined to be pro slavery. That may have been the case in most of the world for centuries, but that wasn't the case in America.
The abolition if slavery necessarily required sabotage of slavery on part of slave owners otherwise not a single one of those states that became free states would've become free states. In other words there would've been no North to participate in the Civil War you constantly re-litigate.
"They had had 11 years to pass abolition laws, yet they were all still slave states."
They had a lot more than 11 years, and Massachusetts wasn't the only state that became a free state, and states like Vermont and those in the Northwest came into the Union freesoil-on-day-one because of Jefferson's abolitionist ordinance.
The Northern abolitionists were dead on to hold Jefferson in high regard. Unlike school kids today, there's a high probability that school kids in the 1820s may well have read the full text of the Northwest Ordinance as a matter of course. They would've held the original source material in their fingers.
I sometimes think we talk past each other. They only had 11 years from 1776 to 1787 when the US Constitution was written. In that time, state legislatures could have passed all the anti-slavery stuff they wanted but they didn't. The only state to abolish slavery was Massachusetts, and it did so with liberal legal trickery rather than an actual vote of the people or the legislature.
Vermont wasn't a state when the Declaration was written and it also wasn't a state when the Constitution was written. It was an independent Republic until 1791.