there is a difference between sharing and stealing posts. On G+ when a post is shared, people(with whom the post has been shared) can see the name of the creator of the post. The original creator's name appears in each and every post that has been shared or reshared. And I'll tell you why this is important. G+ does not work like facebook. I just don't want posts to be shared randomly without people knowing I created the post. For eg : Suppose I am good with 1 min tips to maintain your health and I post articles and tips to create a follower for myself. I may have different reasons in wanting to create a circle of followers for myself. Could be for business purpose like self promotion or something like that. So if you share my posts, I would be happy. I may even thank you for sharing.
But stealing here means, not sharing but copying the exact content I have created(I may have invested a lot of time doing research for that particular post) and posting it as an original post of yours. So if that post is reshared your name appears as the original creator of the post.
so that would beat the purpose of me creating the post. And by post we mean some useful and engaging articles, not just another party photo or an status update.
P.S- I think you might not have read the article before commenting or maybe you just read half of it (common habit of of people who still enjoy using fb) as the author has clearly mentioned in bold, that posts can be +1ed, commented on, or shared. All he asks of us is not to steal a post. I don't see any reason not to comply with that request.