So the GOP outvoted the dems on the CRA.

There were more Democratic votes for the CRA than Republican votes - in both the House and Senate. But there were also more Democratic votes against the CRA as well. The biggest political faction in favor of the CRA were liberal Democrats, which were numerous than the Republicans; but the biggest faction against the CRA were Southern Democrats.

But none of that is relevant to my point. Southern white conservatives overwhelmingly opposed the CRA (and they were largely Democrats at the time, but now they're overwhelmingly Republican). You raised the argument that demographic groups can culturally change - that just because the modern GOP is the home of Southern white conservatives doesn't mean that those Southern white conservatives necessarily do/would have opposed the CRA. But LM's argument (which you've just repeated) commits the same category error that you think is wrong. Just because the folks who were opposed to the CRA back in the mid-1960's were mostly Democrats can have zero bearing on which party today would be the predominant supporter of the Civil Rights Act - or indeed which party at the time was the driving force behind passage of it. The truth is that both the majority of support for the CRA and the majority of opposition against the CRA were both Democratic - mostly because Democrats had so large a majority of the seats in both chambers that they contained within their caucus nearly all of the political spectrum

I think what also played a big part in coloring people's perceptions is what happened around the Civil Rights Act. The biggest group in favor of the bill was (again) the pro-CRA Democrats. Although the Southern white conservative faction within the Democratic party led the charge against the CRA, the political dynamics painted a very clear picture which party institutionally was supportive of Civil Rights. Immediately after the law was passed, the GOP chose a Presidential nominee who had opposed it (Barry Goldwater). Some very high profile Democrats switched to the GOP because they were so upset with Democratic support for Civil Rights - most notably Strom Thurmond and Jesse Helms, but several other southern politicians (including our own Florida governor Claude Kirk). You did not see the opposite. You did not see any of the Republican folks who opposed the Civil Rights Act leaving the GOP to join Democrats in protest of the GOP's support of the CRA.

So while you have several anti-CRA politicians (like Helms and Thurmond) looking around and seeing that the GOP was the place for them, you had zero pro-CRA politicians thinking that they no longer had a home in the Democratic party.