Even if it was just labeled 'dub-con' initially, why would you want to read something so close to non-con if you're not into non-con?

Dubcon is one of those things that can vary widely in tone and content, including enthusiastically lowered inhibitions (sex pollen, heat, drugs), ravishment fantasy, power differentials, coercion and manipulation played seriously, and more variations. It's common to like one of those flavors but not the others, and with some varieties, a reader's line between hell yes and fuck no might be thinner than others. It's usually pretty easy to tell early on which one an author is going for, but it still doesn't hurt to tag the borderline cases carefully.

That doesn't justify a reader attacking an author over a difference in opinion surrounding tagging, of course, but as I see it, that's not what happened here.