The way I see it, as long as they're building cars now to test, what's the harm if the cars are not built by hand, but rather by an almost complete production line? They will still catch the same problems, if not more, considering people generally think production line is more prone to quality variability than hand build.
Maybe Tesla instead of saying they're skipping beta, they should have said
"yes we're building beta now as planned. In addition, our production line is almost complete, so we thought might as well just build the beta using the production line. If we find anything that needs to be tweaked, our production line can be quickly changed. [add some color on how automated and flexible the new design of the production line is] By July, we'll be ready to build early production version on a production line that is already proved out and ready to go."