Because unless you are drawing a line at an amplification level of "infinity", that seems like a distinction of degree, not type.
I don't agree. Transportation experts categorize even the most sedate bike riding (a Dutch bike on a flat path) as active mobility and driving a car or taking the bus as passive because riding a bike involves a kind and quantity of physical movement that is simply not present in driving a car – exercising balance by leaning into turns, getting a baseline amount of leg-pumping, occasionally needing to exert hard force to, say, catch a light. This sounds pretty mild but produces a multitude of cascading health effects. I'll even take the bait and say you should steel-man your fitness-as-virtue argument: we're analogizing physical health to mental capability, not as an arbitrary dimension of person-worth, so it makes complete sense in this context to prefer the healthy option.
Kay also specifically calls out the quality of being able "to go flat out with [the rider's] body". This scaling-up-with-your-effort ability of the tool is especially enlightening for the analogy: programming languages have it, spreadsheets have it, scientific calculators kind of barely have it, whereas dumb calculators, CSV, and most low-code tools do not have it. The former accept almost arbitrarily complex mental input and do work on it that feeds a feedback loop, the latter force you into a narrow band of input and often only amplify it in specific predetermined directions.
We have to be political about our computing tools, and generate tools the use of which results in "better" people?
We should steel-man this line of thought as well. I think you're reading it precisely backwards, as authoritarian control of mental tools. To that we would say no. It's about enabling people to be better by giving them more power over the tools we build, to which we should say YES! Yes, when we build tools we should allow people to do more things than we specifically intend with it. It's good practice in software and perhaps even a moral quality demanding it for end users. Think of how valuable it is to have escape hatches like passing a function argument to define behavior in someone else's code, or to have macros available to create DSLs, or to occasionally be more verbose so to eke performance out of a hot loop, or to have a programming portal in a GUI to provide a more nuanced side channel.