I thought it puzzling. I checked it out. It's actually an inaccuracy in the posting of imdb. Wrong Sergio Leone and Robert De Niro film.
Once Upon A Time In The West was one of the 25 most dangerous for Premiere. It actually would of been a compliment I guess. The category is described as:
These are movies about which you could say, "That's Not Entertainment." They're not "rides" or "diversions." They are galvanizing experiences that place squarely in your face all the stuff Hollywood usually presumes you go to the movies to get away from. Films that rearrange your head, that challenge your bedrock ideas about life and love and the big sleep. Consciousness-expanders, in other words, but rarely in a pleasant way. Thank God for them. The entire list was:
Bonnie And Clyde
Boys Don't Cry
In The Company Of Men
Dead Ringers
Eraserhead
Gimme Shelter
Happiness
Bad Lieutenant
M
Once Upon A Time In The West
A Clockwork Orange
Repulsion
Requiem For A Dream
Reservoir Dogs
The Sweet Hereafter
Taxi Driver
Blue Velvet
Dancer In The Dark
Freaks
Peeping Tom
The Lost Weekend
Natural Born Killers
Romper Stomper
Un Chien Andalou
Weekend
Link for their list is:
http://www.premiere.com/best/3593/the-25-most-dangerous-movies-ever-made.html