I was taught racism is bad, and in the literal sense that is an opinion, its just one that our society takes for granted now.
I do agree that the best counter for bad ideas is talking about better ideas and comparing them. Which, to the point of the article, is the crux of critical thinking skills.
I'm not saying that my trek through public school was free of political indoctrination. DARE drug education was pervasive. There is a big difference between "drugs are bad mkay..." and "you're white so you are inherently racist".
Schools are always mouthpieces. Where I grew up in the 90s in Southern California, the public high school I went to was proud of the fact that they'd figured out a way to have a school-funded evangelical christian club that met weekly on campus (and had hundreds of members). My English teacher taught a class called "Bible as Literature" which was overtly religious even thought it wasn't supposed to be, and she was well-known to be a born-again christian. The P.E. teacher at my public middle school used to make us all stand on our numbers while he told us stories about how Jesus got him through his time in the Marines.
None of this is great, but it's just the way life is, and I believe it's important for my kids to understand, in context provided by my wife and I, how society all fits together. School is an important part of that, in my opinion.
Funny I thought that was all that school was supposed to do.