3-D doesn't quite work that way. Each of the two lenses in a pair of modern 3-D glasses is polarized in a different way. One is polarized vertically, the other horizontally. These correspond to two different projectors, each projecting a slightly different image (one for the left eye and one for the right eye), and each with either a vertical or horizontal polarization filter. So, when you wear the 3-D glasses, the left lens only allows the correctly polarized "left eye" image through, and the same with the right eye. Since each image is slightly different, the brain connects them and produces the 3-D illusion in the process.
In order for the whole process to work, each eye has to be completely covered by the correct, different polarization filter (glasses lens).
Hope that wasn't too confusing.