One of the points Ed Feser made and made well in The Last Superstition was that there's a kind of shell game going on with the word "science". The short version is that when many people say "science shows...", what they really mean is something closer to "science + these metaphysical/philosophical commitments (which I, the speaker, may not even be aware of holding to) says..." Notice that the difference there isn't just between "science" and "science + these metaphysical/philosophical commitments", but between "shows" and "says".
Now, Ed argues that science takes certain metaphysical/philosophical claims for granted, simply to get off the ground. I agree. But I also wonder if this goes far enough.
The demarcation problem does not get talked about enough. But my own view, put shortly, is this: Once we sit down and strip away from "science talk" all the smuggled in metaphysics, the unwarranted assumptions, the appeals to authority and consensus opinion, we are left with a core set of knowledge and methods with these two defining traits:
1) Of tremendous practical use, particularly with regards to technological and strictly empirical problems.
2) Of basically zero use in determining the answers to, or even making much headway with, most of the "important" questions of philosophy, theology and metaphysics.
And this is to say that science is "compatible with" a shocking range of positions and views. From idealism to dualism, from panpsychism to hylozoism, from polytheism to deism. Science, as science, is even compatible with scientific anti-realism.
I'm being brief here, glossing over things. But why do I bring this up? Well, because scientism is commonly thought of as being a fanatical devotion to science, or attempting to apply science to problems or questions where it is supposedly inappropriate to do so. I not only reject that definition, I consider it downright deceptive.
My own view comes closer to this: Scientism is the habit of passing off various non-scientific, philosophical or metaphysical claims and conclusions as science. It is the express abuse and confusing of science.
People engaging in scientism don't hold science as science in exceptional esteem. They hold the imagined authority (intellectual or social) in high esteem. In reality, they are deeply dissatisfied with science as science, precisely because it does not or cannot do what they desperately wish that it could.