We do encourage each other. If this person were signed up for a half, or even just the full, we would all be very encouraging. I truly believe anyone can do a half marathon with training, and if you have the commitment, you can do a full. If they were signed up for a half, you wouldn't see a single negative comment. If you they singed up for a full, there would be a few "here's what you are in for" posts, but nothing saying they couldn't do it.
But Dopey is called Dopey for a reason! It is not meant to be a first race ever. It is not meant to be a first marathon. It is meant as a "challenge" to serious runners. I just can't bring myself to encourage something if you really aren't ready for it. I say the same thing when people go out on a half course with only 3 miles of training. It's just dangerous.