Education and education research are experiencing increased digitization and datafication, partly thanks to the rise in popularity of massively open online courses (MOOCs). The infrastructures that collect, store and analyse the resulting big data have received critical scrutiny from sociological, epistemological, ethical and analytical perspectives. These critiques tend to highlight concerns and/or warnings about the lack of the infrastructures' and builders' understanding of various nontechnical aspects of big data research (eg seeing data as neutral rather than as products of social processes). These critiques have primarily come from outside of the builder community, rendering the conversation largely one-sided and devoid of the voices of the builders themselves. The purpose of this paper is to re-balance the conversation by reporting the results of interviews with 11 data infrastructure builders in higher education institutions. The interviews reveal that builders engage deeply with the issues the critiques outline, not only thinking about them, but also developing practices to address them. The paper focuses the findings on three themes: designing a productive science, navigating ubiquitous ethics and achieving real human impact. Researchers, policymakers and infrastructure builders can use these accounts to better understand the building process and experience.