Funny thing about that movie, which is one of my favorites BTW and mostly because of James Earl Jones who I'd pay to read a car's owners manual, but the protagonists are obviously hippy holdovers from the 60's and liberal to the bone, however, there are moments when they are really conservative in their thinking and Costner's performance, while not that great, isn't bad but James Earl Jones & Burt Lancaster and even though they got Joe Jackson wrong(he batted left but in this movie he batted right), Ray Liotta in his pre-Goodfellas performance isn't bad either. Watch it. It's a good popcorn movie.
There are a dozen better baseball movies, but you're correct it is an entertaining movie.
The guy who wrote the book on which the movie is based is/was a complete Shoeless Joe Jackson apologist who thinks he was railroaded when he was banned from baseball. In addition to the batting from the wrong side, Costner kept telling his daughter that Jackson still batted .367 in the series and even hit a home run (rare in 1919) even though the White Sox threw the series.
All of that is true, but it has been forensically analyzed and Shoeless got most of his hits in the games where the Black Sox were allowed to win. In all the games they lost, he was terrible.
The great baseball writer Bill James summed this up thusly (paraphrasing):
People who think Joe Jackson deserves to be in the Baseball Hall of Fame are the type that also are rooting for the cute murderer