I don’t assume that intent is necessary. I did assume that intent is sufficient. The reason for my assumption probably has to do with how the words of the posuk are phrased. “Lifnei iver” always makes me picture something like Lucy holding the football for Charlie Brown-
a deliberate act of cruelty. It just seems to be the penultimate way of causing another to sin. It’s hard to imagine that the guy who deliberately e.g. puts treif candies out at a kiddush isn’t over even if no one eats. Mainly a feeling. You disagree?