Take two students in the same class searching "climate change" for a project. One gets NASA and IPCC reports; the other, because of a parent's browsing history, gets denial blogs. That's not relevance—that's segregation by algorithm. You're right that no ranking is perfectly neutral, but that's an argument for making the process transparent and consistent, not for letting it silently adapt to each user. The bias is still there, but at least an unpersonalized bias can be studied, criticized, and fixed. Personalized bias is invisible and unfixable. That's why stripping it out is the honest move.