I took this quote to mean the following: Engineers are well equipped and positioned to understand the set of solutions that are available to them and the material negative impacts of those solutions (e.g if we build a dam at spot x, the region y might have an increase in floods). But engineers should not be given the ability to make decisions about which of set of negative impacts a society should bear, and that should instead be a decision made collectively.

So the interface between the engineers and the people is not to find solutions together, or to find flaws together, but for engineers to find solutions and flaws, and the people to pick the one that they are happiest with.

(I'm not certain my understanding of the quote is right, just sharing my interpretation / an alternative to the ones you shared)