It does no such thing. The law may require that they look both ways, but people are in no way "forced" to obey the law. In point of fact, people tend to follow norms of behavior rather than the letter of the law. The rolling stop is a perfect example of this. The law requires a full stop, but cars and bicycles alike, by convention, do not come to a full stop if they think there is no other traffic at the intersection.

I've heard it suggested that safety would be increased by actually removing the signs altogether in many situations because it would force people to actually think about what they had to do. (See Tom Vanderbilt's fascinating book, Traffic, for instance.)