I propose calling it Implementation Success Bias, or maybe just Expected Success Bias.
There is a much more serious subset of this when people maybe-consciously look at the worst possible outcome of their opponent's view, and then claim that their opponent is eeeevil and specifically desires that outcome.
I have to say I agree with being annoyed at how whenever people have a Great Idea, they tend to COMPLETELY ignore the actual implementation of the idea (often jumping to considering problems once the idea is implemented).
Is there a name for the (I claim) extremely common practice of blithely and unconsciously always looking at your own view (political especially) in terms of its best possible outcomes, while always characterizing an opposing point of view by its worst possibilities?
If not, I think there should be. It seems like a major major source of unfruitful argumentation.