misterpessimistic: I dont see why a freethinker would have a problem with tradition. If it works, it is fine.
Where my view of tradition starts to conflict with most freethinker views of tradition is that I'd say it's something a good idea to err on the side of tradition even when the reasons for doing so aren't obvious.
The change in American diets makes for a pretty good example. We didn't know, 50 or 60 years ago, what effect it would have to abandon traditional dietary norms. Traditions exist for complex reasons, and we aren't always capable of seeing all of those reasons at the moment of decision. And now that we can see some of those reasons in retrospect, we find that it isn't all that simple to revert tradition. We've lost some memory of the traditions that stood, and we've restructured our society in ways that make those traditions difficult to sustain, and to some extent, we're just really used to our new ways and don't want to go back.
That isn't to say that we shouldn't part with tradition when we have very compelling reasons for doing so. But we have to balance the weight of those reasons against a certain respect for tradition. "We've always done it this way," shouldn't trump all arguments, but it should suggest, at least, that a given tradition survives for a reason, even if we don't see that reason straight away.
And as an aside, slavery wasn't exactly traditional when it was adopted in the U.S. It was an innovation, both in the sense that Europeans hadn't practiced widespread slavery since the fall of the Roman Empire, and in that American slavery differed from Roman and Hellenistic slavery in some very important essentials. Nor do I think that American slavery was often defended by the argument according to tradition.