Supposedly, a meltdown at sea is pretty low risk because you have the perfect heatsink literally everywhere around you, and its a molten salt design, which I think(?) (source: my ass) means that the fuel would at worst leak into the sea and immediately solidify back into some inert state.
It’s based on assumption, not faith. If we can trust our senses, and if things will continue to be as they have been, then the things we are learning have value. As long as you can recognize that everything could in theory end or completely change at any moment, it’s not blind belief.