I always see conservatives deny the party switch and say that democrats are still the party of slavery. Most reasonable evidence that I have looked into would say that they are wrong. When I try to discuss they always say that the geography of the parties switched and not the beliefs. Then they will say something about people moving north or south post civil war. I have yet to find any significant information that would reinforce their beliefs. Is there a possibility that they are right?
Yes, the parties have evolved and realigned since the Civil War. Some links from the FAQ:
Yes it was very real, the Republican and Democratic parties completely switched their stances on social issues, primarily on civil rights/race, in the last century. 160 years is a very long-time in political history and to say the Democrats in 2020 are the party of "plantations and slavery" while the Republicans are the party of "freedmen and emancipation" is simply ridiculous and a cheap-shot.
The beginning of the racial "switch" between Democrat and Republican I would first attribute to 1948 when Democrat president Harry Truman desegregated the Armed Forces. This was the beginning of an alienation of pro-segregation Southern Democrats, and many left the Democratic Party to become independents. Ex-Democrat Strom Thurmond was one of the first Dixiecrats to run in 1948 as an independent on a platform of states rights and segregation. He remained in the Democratic Party until 1964, when he formally left in opposition to the Civil Rights Act.
Fast forward to the 1964 Civil Rights Act by Democrat president Lyndon B. Johnson and this outlawed segregation on a federal level. However it alienated Southern Democrats further, and in the 1968 election George Wallace carried many Southern states running as a Dixiecrat and the Democrats lost their hold on the south. The Barry Goldwater campaign in 1964 ran in opposition to the Civil Rights Act, however Goldwater voted against the Civil Rights Act not because of racism (he was pro-desegregation) but because he believed it was federal overreach and the Republicans favored states rights. However for Southern Democrats "states rights" was cover for racist pro-segregation policies.
This is when the so-called "Southern Strategy" was initiated by the Republicans to gain the support among former Southern Democrats who left the Party because they were displeased with the Civil Rights Act and path of the Democratic Party in general on other social issues such as immigration. For example, the 1965 Hart-Celler Act by LBJ allowed unrestricted immigration from non-White countries for the first time, as opposed to just Europe, and this permanently changed US immigration demographics. Now the largest pool of immigrants were arriving from Latin-America, Asia and Africa.
During the 1968 election, Wallace carried most of the south however Nixon won the first few Southern states for the Republicans, and since the 1968 election no Republican presidential candidate has received more than 13 percent of the African-American vote. As of 2020, it is now in the low single digits. The last election Democrats carried the South was with Georgian-born Jimmy Carter in the 1976 election, and later on in the 1990s another southerner from Arkansas named Bill Clinton won a few states in both of his elections.
When it came to racial equality and support for civil rights in the past century, the Democrat and Republican parties did a full-switch.