If I'm not predicting and anticipating things happening, I'm not really getting much out of the story. The edge of the seat feeling has been taken away so it feels like it's not really worth spending the time.
Oddly enough this somehow still works fine for things I have already seen and thoroughly enjoyed - for example I could go binge Breaking Bad twice in a row at any time, no bother.
I guess in that case I'm looking forward to the great plot points and storylines I know are coming, but if something of unknown quality has been spoiled then I don't know the journey is good enough to plow through, so there's no anticipation and no dopa to be mined.
In summary spoilers take away the dopamine so there's no longer any drive or desire to begin consuming it in the first place.