My thought on this comes from a good chunk of direct experience: I've taught a number of courses to undergrads at NYU, as well as having about 5 summers of teaching experience in programming and cryptography at summer camps including CTY.
Imagine all students are given a button that says "give me an A," and they can press it if they choose, or do all the course work and possibly get a worse grade. Even if you chose to do the work because you were self-motived, you'd still be tempted to press the A button to guarantee a good grade.
That's an exaggeration, but the point is the same. The easier it is to get _any_ kind of validation without real work, the harder it is to learn.
It is harder to stay motivated, and the feedback received becomes less meaningful. It is even disappointing to simply know many of your fellow students probably cheated without consequences.
I do believe in seeing answers after doing the work, but it is just common sense to avoid posting them before things are due, and to support clear communications between the instructors and students about the details of posting answers.
First of all, cheating is really easy on Coursera without having to appeal to public solutions posted by somebody else. You can get private help without anybody knowing anything about it and you can do so in a really efficient way, since there's absolutely nobody watching you.
Coursera courses are for people willing to learn something, providing certificates was stupid in the first place, poisoning the well for everybody that's there for the right reasons. The topics are not exactly PhD-level, you can probably find 80% of all the answers you need by doing stupid Google searches and even if we were talking about PhD dissertations, cheating is still possible, the only difference being the difficulty threshold.
That cheating is so easy on Coursera, "give me an A" is precisely what's going on for people that are there, not for the learning experience, but for an A.
Which is why the value in these courses is only for personal growth and personal gratification. I would never look at such certificates on a resume, because such certificates are even less valuable (from a market perspective) than a piece of toilet paper, because at least a piece of toilet paper is useful for something while at work. And no, interest in subjects such as "Scala" is not enough, because such proxies for performance can be easily discovered and hence gamed.
Also, the gratification comes from knowing that you worked and that you passed the tests. The certificate only holds personal value if this condition is met.
And in the context of Coursera, that certificate does not make sense anyway. If you follow the forums, you'll get a lot of people asking if they can still join the course with late submissions, providing reasons for why they are late in the hope that staff will make exceptions (they've taken long trips, the dog ate their homework, etc...) - which is just a mindbogglingly dumb thing to do.
Maybe the 'A' or nice cert is there for some people, but no one that I know personally cheats for the grades on coursera. OTOH, all 7 of them are currently well employed software engineers, so maybe the incentive to cheat just isn't there for them in particular. Until the signal gets gamed, I think it will be useful for hiring. Further, it's pretty verifiable if the interviewer has also taken the course. What did you think about the programming assignment about X for course Y, how did you do Z? Throw in fake X for real Y if you are particularly suspicious. If you've cheated through it, it's gonna be obvious.