There's an unwritten code among movie critics that even if you hated a movie, you don't spoil the ending in your review. If you feel you can't adequately explain why you loathe the film without also describing its finale, then at least you warn the readers that spoilers are a-comin'.
But what if a film's plot twists are so vile and offensive that you feel obligated to warn people away from the movie, "spoiler alerts" be damned? What if being evasive on the specifics would be a disservice to the readers, who might see the film and be as horrified and sickened as you were? Don't you owe it to them to do whatever you can to prevent that?
Splice has struck just such a nerve with some critics. (This post does NOT contain spoilers.) The sci-fi thriller got mostly good reviews when it opened last Friday, but the critics who don't like it REALLY don't like it. Many of their reviews freely mention some specific third-act plot points that would normally be considered out-of-bounds without a spoiler warning. In some cases, those scenes appear to be WHY the critic didn't like the film -- which means maybe it's reasonable to spell it out. Maybe you'd be a lousy critic if all you could say was, "Some very distasteful things happen in the movie, but I can't tell you what they are, but you shouldn't see it."