Why should motorcycle riders never ride side-by-side in the same lane with another motorcycle?

1. It eliminates lateral escape room if one rider needs to swerve suddenly to avoid a pothole, road debris, or opening car door
2. It is acceptable because two motorcycles together are the width of one car
3. It improves safety by making the pair more visible to other drivers
4. It is only a problem at speeds above 80 km/h