It falls apart in that a guide is in a business relationship, and that adds a distance that isn't there for parenting -- in that sense a parent can be more of a friend.

But one way parents are not like friends is that friends choose each other, and can drift apart. Parents have a much stronger motivation to keep a close relationship with their kids even as interests diverge, personalities may not mesh terribly well, etc..

The important aspect I wanted to touch on, though, was more about "authority" vs. "friend", and in that balance I think a parent should fall much more on the friend side.