Earlier quoted context omitted.
Because it leads us down seemingly useful paths that are in fact dead wrong. There is only physics, but at some levels it more convenient to ignore the physics (what is happening in the body) and to describe our experience. Rovelli is a reductionist, the only logically and physically defensible intellectual position, while dualism is inherently supernatural, invoking phantoms, phenomenology that is purely fictitious.
Ok, but that doesn't really address "pernicious". I understand pursuits of philosophy are inherently concerned with truth, but does not truth mean pernicious? My experience of reading philosophers is limited; is Rovelli just a materialist and that's that? Is this positivism?
My understanding of positivism is, in a nutshell, that its goal is to reduce everything to physics, including social, inter-personal interactions. My read of the article is that Rovelli is focused on the intra-personal, so to that extent it isn't positivism, or is at least a limited, focused positivism. Extending Rovelli's thinking to the inter-personal would be, IMHO, a categorical error: While we may one day be able to fully describe the physics (and electrochemistry, etc.) of everything inside the person, physics is insufficient to describe what happens between people, at least to the extent that what is happening is a result of each person's actions, choices, etc.
I think this where bringing qualia in as a level of abstraction is useful: Everything about us is ultimately operating on our physical hardware, but not everything about us is "just physics", since our "us" (our OS, if you will), makes observations and chooses actions that are determined at least to some extent by the "us", and not just by the physical operations.
At this point, one could bring in Skinner and make everything operational conditioning, or Kahneman for a slightly different take where much of what we observe or consider consciously (the energy-hungry slow system) has been pre-filtered by physical processes that are not available to us (the energy-efficient fast system).
If those lines of thought are correct - and that remains an open question - then we could potentially arrive at a complete positivism wherein everything is determined primarily by our internal physics, though we wouldn't get predictability for the same reason that we cannot solve the three-body-problem analytically or predict the weather accurately for all time or predict with certainty the motions of the planets, etc.: There are too many inter-dependent variables, and modelling will always lag actual behaviour.
I think we are on safe ground saying that intra-body behaviour is all physics, and on safe ground describing some of the physics responsible for what we call thought, e.g., neuropsychological processes, but at some point we need to model things differently to continue to make sense, make progress. We get away from just-physics at higher levels of abstraction, with the challenge being to describe the transitions from one model level to another (corporeal electro-chemistry to reflective thought and action to inter-personal relations to sociology and economy).
Sort of like how we know that everything is quantum mechanics at the appropriate scale, but that QM isn't terribly useful for modelling weather, planetary motion, etc.