Highlights should be reader-specific not author-agnostic
White Feather, you bring up an interesting feature request!
I too think that highlighting should either be an optional feature, OR, readers and authors should be able to turn on or turn off highlights in the text they are reading. Highlights can be useful and desirable no doubt in intereacting with the text, but they can also be very distracting.
Highlights enable readers to interact with the text and change the textual emphasis. In this sense, highlighting helps other readers (and some authors as well) to see where or which passages were marked by readers who accessed them. Besides, for those readers who have grown into the habit of reading any text with a highligher marker, having an opportunity to highlight a text provides them an “organic”, almost “skeumorphic” reading experience that mimics real life paper text reading with a marker in hand or reading a text on a kindle/epub reader. This is seamless experience of reading something on paper, on kindle/e-reader, and on the web. The feature is not new either. For a long time, web apps like Diigo (http://www.diigo.com) have offered highlights for ages.
Diigo - Better reading and research with annotation, highlighter, sticky notes, archiving…
Diigo is a powerful research tool and a knowledge-sharing community
A feature that might be added is something like that of a kindle book; highlights per article be made available or highlights can be hidden or made visible as needed (so, something like “hide highlights”, “view highlights”).