There's an almost absurd level of apolitical thought here.
@Moderate Hero was the closest of you lot to hitting on it. First of,
@NHBL - you're asking the wrong question. Of course there will be a Lost Cause argument of some form. That is literally fucking inevitable. There are pro-Nazi arguments out there, after all. What you should be asking is how such a narrative can be kept from being almost a default one.
Everyone here, but particularly
@TastySpam read this thread.
There was no reconstruction soft or generous enough to appease the plantation elite, because they lost their slaves! The thing for which they fought the war! And
@Skallagrim you have a lot of big ideas on how to prevent a Lost Cause narrative. Trouble is, they all implode the moment someone asks "well how can that be achieved"? Sad!
Here's what you all are missing- the Lost Cause narrative is one strengthened by
institutional power. Groups like the UDC had the money and political power to put up those statues everywhere, to decide what got (and still gets) written in school textbooks. They had the power to force a bogus "reconciliation" in 1876 that turned over the South to the depredations of the old Plantation elite. Here's an alternative solution that will make sure the Lost Cause Narrative is not a powerful one.
There were less than 10,000 households who owned 50 or more slaves. Expel them all from the United States (with the exception of the few of those who served the Union). Parcel out their lands to their freedmen (giving the latter an independent base of political and economic power rather than the serfdom that we euphemistically call "sharecropping"). Do the same for everyone who served as a governor, congressman, or senator of the Confederate States (I'm generous- I'll spare the State Legislators). And do the same for everyone who served as a General in the Confederate Army. There's a lot of overlap between these groups. It would significantly undercut the power of the Lost Cause Myth, that's for sure, and it would elevate those best positioned to fight the myth. Also, keep a major force of Northern Federal Troops, sustained by National Service requirements of some sort, garrisoned there until the turn of the century. In any town where there is an attack on freedmen, "carpetbaggers", and "scalawags", deportation and expropriation of all former Confederate officers is in order.
Thus, the Lost Cause has no institutional power on which to grow. The people who pushed for it hardest are scattered to the four winds and penniless. Oh, sure, it will exist, there will be deadenders out there, but it will be a weak, fringe ideology.