A basic argument for panpsychism, as Strawson presents it, is that we know we are personally conscious. It's the one thing in the world we can be absolutely sure about. If we also agree that we are made of matter, and that we are conscious as material beings, without the aid of "spirit", then the question arises as to how consciousness comes about from our corporeal bodies. Logically there seems to be two possible explanations: 1) at a certain level of complexity consciousness "radically emerges" from matter where previously there was nothing, or 2) awareness is already a property of matter itself to begin with, so that consciousness does not "radically emerge" at a certain point of complexity, but is the extreme end of a continuum of awareness.
If you say there is no evidence for option 2, it's fair to point out that there is no evidence for option 1 either. It's commonly taken for granted that awareness is a special property of some beings, and it's postulated this property somehow emerges from dull matter. There is no prooof for these assertions either.
Some scientists are now devising ways of testing panpsychism, including David Chalmers. Sam Harris seems to find his ideas more compelling that those of Daniel Dennett who once argued that "consciousness is an illusion". They comment that Dennett seems to have modified that extreme position. They talk about panpsychism at around 45 minutes.