>... on the Continent Galileo grumbled at the armchair philosophers who, “in order to acquire a knowledge of natural effects, do not betake themselves to ships or crossbows or cannons, but retire into their studies and glance through an index or a table of contents to see whether Aristotle has said anything about them.”

That quote does not appear to be dismissive of indexes to me. It appears to be about people who appeal to authority rather than doing their own empirical research.

I didn't see other quotes to support the claim that [a significant number of] scholars feared that the index would destroy reading, and I'm a bit skeptical of the claim offhand. I wish there was some information structure that would allow me to find such supporting evidence more easily...