> What’s the negative impact of the recent discovery of a non-quantum recommendation algorithm on the field of quantum computing? Should the young researcher have spent time considering and detailing that?

If we consider the goal of research to improve society, then yes, I think it's reasonable to expect a researcher to spend some time considering whether what they're doing is going to actually improve society. In biology, most funding agencies require you to take a brief (~8-10 hours of class time) course on the responsible conduct of research, even if you aren't doing any human subjects research.

In the specific case you gave of the non-quantum recommendation algorithm, the negative impacts should be more or less the same as the impacts of the quantum algorithm, but with less of a barrier to entry. And even the person proposing this acknowledges: "We all agree it’s hard and that we’re going to miss tonnes of them, but even if we catch just 1% or 5%, it’s worth it."