[jlawson]

The belief that every child has the same natural ability is as radical.

It's radical because goes against all evidence, experience, and common sense - it is ideology taken to a puritanical extreme. There is no more extreme position one can take.

[teiferer]

Though I don't think that's the argument. Even those advocating for the end of the program for gifted kids don't believe that all children have the same natural ability. Maybe some of them do, but the main arguments are different and are not actually that "radical".

And even if that was the argument, the term was used in the context of "radical egalitarianism". So, the argument doesn't automatically transfer to such a radical variety of "egalitarianism" in society as a whole if it focuses on a single aspect.

There are two levels of quite extreme exaggeration here, calling the end of a particular school program "radical egalitarianism". Which words should we use if an actual radical proposal comes along?

[jlawson]

Ending all school programs that separate children by ability is the most radically egalitarian position possible, even in theory. There is no more extreme position one can take.

Given that, there's nothing else to save the word for. This is the limit; the max. So if radical refers to anything at all, it refers to this.