-These laws restricting ballot access in the US seem to date back to -the 19th century. Open primary ballot legislation was apparently -first introduced in in the 1890's. I don't know the full history, but -it certainly dates back further than the 1960's or 70's, once again -you are obfuscating.
Bill, you don't know American history, quite obviously. The laws restricting ballot access were PASSED largely in the 1890s to bar blacks from the primaries, as part of the more general disenfranchisement of black voters passed in that era as legal Jim Crow spread across the South.
The fight to open up the Democratic primaries to black voters was fought specifically in the 1960s. That's what the famous fight over the Mississippi Freedom Democratic Party at the 1964 Democratic Convention was all about. There were a few legal lawsuits over exclusion of blacks from the primaries in earlier decades, along with organizing in a few other states, but the fight to open up primaries was part and parcel of the civil rights movement across the South.
You can argue that fight had its downside of weakening the ideological coherence of the parties, but there's little evidence of that. Even when the parties were quite closed organizationally, they accomodated quite divergent ideologies. The Dems and the GOP are probably more coherent ideologically today, with open primaries, than they were in the past when parties were far more closed.
-- Nathan Newman