For me it's the fact that I've seen this whole spiel a lot of times already, in EVERY DETAIL. Visual programming will save us all. Nonprogrammers should be able to program. Suppressed, blah blah blah. For something so revolutionary, it sure is some awfully-well-trodden ground. And I don't just mean that this is an old paradigm, I mean this
spiel is well-trodden ground.
In a nutshell, it doesn't work. Using Fred Brook's venerable terminology, the essential complexity of programming is too difficult for nonprogrammers. Even if you entirely get rid of the accidental complexity... and visual layout does not do that, it's full of incidental complexity involved in the layout itself... you still can't get non-programmers into a programming situation, and trying to get them into a concurrent programming situation is just sheer insanity.
And we know it doesn't work because it has been tried. Over and over. Ad naseum, as in, yeah, I'm sick of hearing these ideas as The Answer as if nobody has ever heard of these before. Tell me what's different about your solution and all the other people who have tried this.