So you classify all fortune tellers, supposed psychics and the like as con artists? I don't think it's right, though I can see why you could think so. I believe that whether this sort of thing is moral or not depends on intentions behind it. Someone who sells prophecies knowing that they're just making it up is definitely immoral. On the other hand, someone who genuinely believes that these prophecies will come true aren't doing anything immoral, strictly speaking (though he may be deluded, but that's another thing). Lying doesn't matter for the market (indeed, pretty lies are in very high demand), but it makes a world of difference when it comes to morality. It also doesn't matter whether anyone but the deceiver in question knows about the deception.
I don't see SC as taking advantage of anyone's goodwill at this point. They're selling these things to make money, that much should be obvious by this point. Moreover, they don't deceive customers (what con men you mentioned do). You get
exactly what you paid for. If you're dumb enough to pay for a picture, well, you've got a picture. Protecting good people from deception is fine, but protecting idiots from their own idiocy is not.
Of course, that's about selling cards, not the rest of their development strategy. Though here, I think their situation is similar to that fairground fortune teller example. They're the firmest believers of the humbug they peddle. Call them stupid if you will, but this is not really immoral.
Also, I hope you noticed what your argument does with any and all religions. This is not a criticism, but rather an interesting observation on how all the above matters relate to the problem of religious belief. SC has, for many people, pretty much become a religion (it's not alone in this, but a rather notorious example). Just what is the difference between believing Chris Roberts will make his game and that Jesus Christ can keep you from coming to harm? At least the former is alive and still working on it.

Of course, if you're against religion, you're killing two birds with one stone.