The argument for users time is a good point, but I don't think the author was intending that. My point was just that it was not sufficiently argued to be obvious.
However, even that does not make the case that web performance is an ethical issue. It would only do so when the number of users is much greater than the amount of effort it takes to make a site.
If I make a site that I expect 1000 people to look at, then the performance of that site isn't really significant. And not an ethical issue.
There's a categorical imperative aspect to this: a site with 1000 daily visitors (not necessarily unique) is not big enough to make its performance a significant issue. But if all such sites think like this, then it suddenly becomes an issue.
However, even that does not make the case that web performance is an ethical issue. It would only do so when the number of users is much greater than the amount of effort it takes to make a site.
If I make a site that I expect 1000 people to look at, then the performance of that site isn't really significant. And not an ethical issue.