IMHO the riders safety is INCREASED because;
1. His hind end isn't waiting to get rear-ended behind you.
2. his side is well protected by your vehicle/vehicle in front of you.
Lastly...WTF ever happened to simple (formerly common) courtesy? If you CAN let someone proceed in travel (foot, car/truck, bicycle, skateboard, scooter or motorcycle) unhindered, you should do so, as long as no one's safety is affected.
Need more fiber in your diet?