It's misguided, since it's not really being taught to begin with. But both sides support restrictions on curriculum, and speech in schools. So I guess we're all just hypocrites.

There is a finite amount of time in the school day so adding something to the curriculum means something gets removed somewhere else.

(Fundamentally there is the problem of "freedom from" and "freedom to". If the people get spammed with the equivalent of bread and circuses it doesn't matter at all that a few people can speak to the wind about important things.)

So should other things people in general disagree with be allowed in schools? Let's say advocacy for racism, discrimination and genocide? After all those should be free under free speech.

What is taught in schools has nothing to do with free speech. Actually let me rephrase that. A teacher doesn't have free speech in school, just like no one has free speech in the job. A teacher should yeah the school's curriculum. If a private school wanted to reach what you are proposing, it works be their right. But a probiotic school shouldn't be teaching that.