We actually know from many historical documents that were Communists in very high levels of the U.S. government, so it shouldn't shock anyone that there were Communists in Hollywood. And Walt wanted to stop them because he believed that Communism was a threat to the American way of life. He believed that they ruined his ultimate dreams for the studio with the strike. And so he chose to speak out against Communism because he believed it was the right thing to do.
As for anti-Semitism, I don't buy it one bit. Walt Disney did many things to help the U.S. win WWII, and made some incredible sacrifices at the Studio in order to help win that war. And last time I checked, Der Fuhrer's Farce is adamantly anti-Nazi. That said it is quite possible that Walt disliked some people who happened to be Jewish. He may have said some unkind things about them, but that doesn't make him anti-Semitic.
As for sexism, I don't buy that one either. Mary Blair did quite a bit of work for the Disney company including concept art on such beloved films as Cinderella, Peter Pan, and Alice in Wonderland. And when Walt decided to build Small World, he contacted Mary Blair, who had left the Studio, to get her influence on the attraction. And Alice Davis is a Disney Legend in her own right, like her husband Marc.
Now, for racism. I guess that old racist Walt cast a distinguished African-American actor to play Uncle Remus in Song of the South and treated him well. Walt even campaigned for the man to get an Oscar, which he did. The family of James Baskett spoke very highly of Walt. This does not mean that Walt didn't say unkind things about African-Americans. But in that time and era, it does not make him racist. And at least one African-American that I know of worked at the Studio when Walt was alive, and kept his job after some layoffs at the Studio.
Last time I checked there's only been one man who was perfect and that wasn't Walt Disney. But Walt Disney was a good man. Did he demand a lot from those who worked for him? Yes. Was he mean at times? Yes. Did he make mistakes at times? Yes. Was he unfair to people at times? Yes. But that does make him a horrible person. Rather it makes him human.