I've got nothing against the pure 256GB SSD solution either. It's all about your personal needs.
256GB internal storage wasn't enough for me and the 512GB SSD was entirely out of my budget. I absolutely wanted the speed of SSD so the Fusion Drive was the best choice for me.
As is mentioned in a similar thread on this debate, the failure rate of SSD vs HDD turns out to be much closer than most people think, moving parts or not. It's just that SSD is a far newer technology.
What did you need 512GB of internal storage for?