Related question: Should mobile ask for taps on spoilers, not clicks?, but that is about the (deprecated) mobile web interface, not the new responsive design. This feature request is related but status-declined, and I'm not asking for it to be implemented on desktops. Not as many people were using touch screens to browse Stack Exchange back then, and the new responsive design has been explicitly designed to accommodate touch screens.
Now to the feature request itself: I realized there that it's rather easy on desktop to discover how to interact with spoilers; when you point your mouse at it, the contents will appear on hovering over it. This might even happen accidentally; the animation will get your attention anyway. Many (new) users are using Stack Exchange on their smartphone or tablet, where this interaction is simply not possible. As this answer mentions, it just looks like somebody made a mistake and posted an empty blockquote.