That's not the main reason, its actually hygeine. If you come off and graze/cut your legs, the hair folicles can harbour dirt and cause subsequent infection. I raced for about 6 years, week in week out and did it for a while and now have gorilla legs!

I have had it many times and just turn it around. I have been sat at lights on my MTB (I have full slicks) and had a group pull up around me and say "not on that, you are not riding with us". Firstly, they pulled up next to me, not the other way round, secondly, its a public road. Sat with them with about 10kms to piss them off and no matter how fast they went, I sat with them.

Have entered many time trials on my MTB and ride fairly regularly on the road. I enjoy riding past them or sticking with them, pisses them off more than anything. Arrogance is disgusting.