It's fun to read postings by so many people who say that hiking alone isn't wise and then do it anyway. As do I :-)

Some people shouldn't hike alone. They are disasters waiting to occur. Others become much, much more careful and therefore possibly safer than if they were in a group. I think I'm in this group.

And there is the effect, already mentioned, of the group being willing to do something much more dangerous than any would attempt alone.

Over the last 20 years I figure if I hadn't been willing to go alone, I wouldn't have done 80% of the hikes I've done.
I prefer camping alone to camping with a group bigger than 4. It's really difficult to find a truly compatible partner in fitness, interest and caution. I'm blessed to have had a great buddy for many years before job losses and soccer-dad duties broke us up.

It should be noted that the predators hunt the popular trails because of the abundance of prey. If I were a concerned female, I would be armed, and I wouldn't go to the popular places. In this case there is more danger in the crowd rather than less. The only safety in numbers is if you can maneuver to be on the inside of the herd when the attack comes.