1. Speed reading fiction is about as sensible as watching movies in fast forward.
2. Speed reading non-fiction will not lead to much formation of conceptual knowledge in your brain, and definitely not the sort of rich inter-connected learning that we probably read for in the first place.
3. Speed reading where you develop a sixth sense for which parts of, say, an academic paper you should slow down and read carefully could probably be a good thing.
In general, while I used to think there was some sort of prestige attached to how much / how fast you could read, I don't think that anymore. It's how 'deeply' you read that counts.