And if you end up on one of those oversold seats you get all sorts of compensation for it, like [free rebooking or a full refund] plus additional money. Depending on how badly this messes up your travel schedule, you can be owed up to 600 Euros (in the EU) plus free rebooking.

It's not at all the same situation as buying a "ticket" for a rocket that hasn't even been built yet; those funds are going to be spent on R&D with no guarantee of success, and you're never going to get your money back; the best case scenario is you get to take the trip.