> doubting that invention of a cart could cause harm
I think this is where we missed each other. I was trying to address "there is always a corresponding disadvantage", and I think mentally I was interpreting this as "an approximately proportionate downside or externality".
I don't disagree at all that nearly any technological improvement can cause harm.
You denied a claim that "every new technology benefits some and harms others" by doubting that invention of a cart could cause harm. I'm suggesting a way that it could.
> the morality of a use case doesn't have much to do with the efficacy of a technology
I agree, but I believe it was morality that was under discussion, not efficacy.