As a new Tildes user, one of the biggest cultural differences I've noticed between Tildes and Reddit is the lack of identity-driven argumentative discussion. Instead, discussion is driven by interests, knowledge seeking, and personal expression.
Identity politics is an umbrella term
that encompasses identity groups both laudable and vitriolic. For example, it includes civil rights, gay rights, disability activism, fat acceptance, white supremacy, and nationalism. (wiki)
It's my opinion that you can't have a rational, cooperative discussion until you set aside identity groups, and I like this aspect of the Tildes culture. I don't want to jinx it, but I believe the lack of identity politics is what people mean when they say they enjoy the high quality, non-divisive discourse here.
It's worth noting my subs of choice on Reddit were /r/samharris and /r/stupidpol. The former encouraged objective, rational discussion. The latter had lots of news that cut though the identity politics of the mainstream (though with a Marxist bent).
I would love to hear the thoughts of the older Tildes users before the most recent Reddit exodus (from where I come).