I believe the general misconception with mesh goggles is people concern themselves with goggle failure instead of the real issue which is the bb's. Most mesh goggles on the market are safe to keep bb's out, whole bb's that is. The safety issue that is not a factor in those that use the mesh devices is, as was posted previously, the fractured bits and pieces of lower quality bb's.
Our club doesn't allow mesh eye protection on the field. We warn others as often as we can. You can't stop people from shooting cheap bb's, but we can stop them from wearing inadequate eye protection.