My experience “in the olden days” with the PDA’s like the iPAQs and PalmPilots, is that not the tip of the stylus itself caused the scratches. The scratches were caused by dust, that gets between the screen and the stylus tip.
By being careful by often cleaning your screen and always cleaning the tip of the stylus before using (I remember the disgusting habit of licking the tip like people long ago did with their pencils), you could reduce the risk of scratching.
The problem however is, that once in a while you either forget to clean the tip or the screen, and there will be a tiny hard spec of dust (silicone from sand or clay) and you will get scratches on your unprotected screen.
.
.