I'm not sure the distinction is as clear as you're making it. It's not like NASA ever really built rockets. Rockwell International built the shuttle for them. They just set the spec and take bids, like any other government agency. The question is a somewhat less dramatic one: should the government specify the rockets it wants and get aerospace companies to build them, or should it let the aerospace companies build whatever they want, buy the products that fit best and make it work? For what it's worth (not much) my own view of the situation is that launch vehicle tech has progressed to the point where the latter approach is likely to save some cash. But let's not act like it's a difference between some free-market fantasy and a soviet design bureau.