@coopey despite it being a bookmark, pnut still uses it for visibility, appreciation. API is only slightly opinionated, and the idea is to let people build on top however they want.
@coopey star is totally arbitrary. like/favorite have issues around "do I do this action only if I liked it? what about cancer/war/etc?" bookmark has a clear purpose, and doesn't suggest the other purposes. Upvoting, visibility, appreciation.