First of all, as has been repeatedly pointed out, Ecoscience had multiple authors. Taking statements from the book and attributing them directly and solely to Holdren is ridiculous, unless it is a collection of single-author essays, which I have found no evidence of it being.
The quotes from
Ecoscience consistently make clear that they are discussing possibilities (based on the thesis that Earth cannot sustain continued population growth and industry, which may not be true on the timescales they were talking about, but is probably true on larger timescales), and they are not necessarily discussing their own policy preferences, but rather solutions to this perceived problem.
These eugenics thought experiments have been in the philosophical literature at least as far back as Plato. Some people like to malign Plato himself because of it. Personally, I'm content to dismiss out of hand most of the proposals, while recognizing that there are some important issues raised, even if the proposals themselves are almost always ethically dubious, disturbing, or disgusting. The main difference is that Plato's thought experiments were focused on achieving political ideals, rather than mitigating perceived, potential ecological problems.
Adding a sterilant to drinking water or staple foods is a suggestion that seems to horrify people more than most proposals for involuntary fertility control. Indeed, this would pose some very difficult political, legal, and social questions, to say nothing of the technical problems. [this goes on to explore the possibility of probabilistic fertility reduction rather than outright sterilization]
It doesn't appear to me that the authors are convinced that the proposals they discuss (and let's be honest, this is just a compendium of ideas that previously existed; it's not as if the authors invented these proposals) are both legal and ethical.
(page 786) ...responsible parenthood ought to be encouraged and illegitimate childbearing could be strongly discouraged.
Note the difference in verb forms. Clearly his preference is for responsible parenthood (don't we all have that preference?), while the rest of what he presents is a thought experiment into possible options the government could take to improve child welfare.
From the page's commentary: "In the final sentence of this passage, Holdren speaks approvingly of Singapore's infamous totalitarian micromanaging of people's daily lives. " I can find no obvious statement of approval of such schemes in the text, and any implicit approval would be contingent on there being a population problem, which the authors may assert elsewhere but is certainly subject to scientific challenge.
Evidently all the critics of Ecoscience are unfamiliar with the concept of using thought experiments to brainstorm for solutions to existent or possible problems. The scanned pages continually make reference to the fact that these proposals are designed to address the problem of unsustainable growth; if in fact population growth is nonexistent or perhaps becomes sustainable through scientific breakthroughs, I see plenty of evidence that the authors would not support any of the socially disruptive mandates that they examine as possibilities in the book. Take this quote, for instance:
It is often argued that the right to have children is so personal that the government should not regulate it. In an ideal society, no doubt the state should leave family size and composition solely to the desires of the parents.
If you want to debate this issue seriously, you're going to have to suppress your knee-jerk reactions. I have knee-jerk reactions to reading some of the passages, as well. For instance:
If this [planetary ecological control and population control regime] be accomplished, security might be provided by an armed international organization, a global analogue of a police force. Many people have recognized this as a goal, but the way to reach it remains obscure in a world where factionalism seems, if anything, to be increasing. The first step necessarily involves partial surrender of sovereignty to an international organization. But it seems probable that, as long as most people fail to comprehend the magnitude of the danger, that step will be impossible.
Of course I hate the UN with a passion, so this starts to make my skin crawl. However, note the last sentence, where it talks about a substantial danger [of ecological destruction and overpopulation]. Most people, Erlich and Holdren included, do not want to impose mass sterilization and strict ecological controls just because they feel like it. They offer the kind of theoretical ideas in the book simply because they want to avoid having us poison and starve ourselves.
Any criticism of Erlich and Holdren (and indeed most radical eco-rights and population control advocates)
must start by addressing this concern and showing that it is ill-founded on relevant timescales. Otherwise you're just wasting your time, because you haven't established any agreement about what the problem is, whether it exists, and on what scale.