I don't claim that addressing anxiety is the only reason to say "Signup in 30 seconds." However, data about what converts better isn't a reason. Conversion data gives you correlations, not reasons for the correlations. I prefer to work from a theory of causality when I'm deciding what to put on the page.
That's an entirely valid point and for the most part, I agree. Where we seem to differ is where we feel the balance exists between correlation and causation. I feel the former still gives very strong contextual direction, and this shouldn't be ignored, especially when the proposed solution is the 'and then what' flow.
I'd actually love to see some studies of how that works in practice, especially given that screen real estate is so valuable around the signup call-to-action. You may be on to something!
