The point is, anyone that can afford it should go for it as every period comes with its own opportunity and not because there is no going down again or not.
As long as people dollar cost average their entry points, it doesn't matter at what price they buy.
Even if you bought near the all time high levels last year, if you bought the market down to where we are today, your break-even point is probably around $10,000 now, and will continue to drop as you accumulate below $7000.
I get it that people might not have all that much confidence in the market right now, but I would do everything I can to not make myself wait for the price to reach +$18,000 again to break-even. It's called torture.
It might take a few more years before the price breaks through its previous high, and when that happens you haven't achieved anything. If you buy now you'll be able to profit by the time, isn't that a solid deal?