Extremism is still just a political viewpoint. It's not inherently more wrong than the others. You're saying Google should impose popular US culture and politics on the world. Including taking sides in conflicts between other countries. It's pretty arbitrary and could easily be wrong.
If you're worried about kids, better ban violent movies, video games, the news, and angry music. No, people have tried "think of the children" before but the children turned out fine.
Extremism is political, but it can't be reduced to a simple difference in viewpoints. Cultural/moral relativism, beyond being a bit of a dead end philosophically, can certainly result in an inaction that opens the doors to political degeneration, anti-social behaviour, and terrorism.
As for other forms of media, we do prevent kids from accessing age-inappropriate stuff, more or less in line with developmental psych research [see: Huesmann, Moise-Titus, Podolski, & Eron (2003)]. YouTube is the odd man out here. The handwringing apologia over the appropriateness of a child entertainer using ethnic slurs would be laughable in any other medium.
Google has famously taken a stance on not being evil. It'd somewhat undermine this goal if it were unable to determine what evil is, and isn't.
Anyone that writes code connecting a query to some media content is in "the business of telling people what to think and control opinions" whether they like it or not. The concern is doing so responsibly.
If you're worried about kids, better ban violent movies, video games, the news, and angry music. No, people have tried "think of the children" before but the children turned out fine.