This paragraph was intended to speak to the relevance of this argument given that (as you say) we can’t easily advance all progress uniformly:
And it may have some uncomfortable consequences. If advancing all progress would turn out to be bad, but advancing some parts of it would be good, then it is likely that advancing the remaining parts would be even more bad. Since some kinds of progress are more plausibly linked to bringing about an earlier demise (e.g. nuclear weapons, climate change, and large-scale resource depletion only became possible because of technological, economic, and scientific progress) these parts may not fare so well in such an analysis. So it may really be an argument for differentially boosting other kinds of progress, such as moral progress or institutional progress, and perhaps even for delaying technological, economic, and scientific progress.
This paragraph was intended to speak to the relevance of this argument given that (as you say) we can’t easily advance all progress uniformly: