It's not the case that all credentials are worthless -- but it is the case that a Coursersa "statement of accomplishment" is. If you take a Coursera course, it should be for the interest of learning something, not for the credentials, because nobody will ever care about those credentials.

(I suspect the point of what they're doing here is to make it so people will care about them -- if you can't get the credentials for free, it makes them rarer and therefore more valuable maybe eventually.)