Maybe they should all just train and race indoors.
Seriously? Have you been to Italy? There are tunnels everywhere. There are dark tunnels anywhere there are mountains or hills. I've ridden through them here in Washington and when I was in Colorado I had to ride through some there too. They aren't real pleasant and vehicles can get a bit close but if you want to ride on some roads they are necessary.
Pro riders have been killed on straight roads in the middle of the day. Drivers don't always pay attention and since they are out there sometimes 30-40 hours a week on a bike they are going to have a lot more encounters than recreational riders.
I feel bad for Horner, he is an exciting rider to watch. We had an Olympic selection race here in Seattle back in the mid-90's and this fresh faced kid lit the race up. He ended up not winning but he was the rider of the race. Been a fan ever since. Hope he recovers soon.