I don't think there is one right or wrong answer; it depends too much on the person's abilities, their amount of experience & preparation, and their goals. If a person is prepared and stays within their limits, they will be safe probably more than 99% of the time. This lets people choose whether they go solo or with people. I tend to think the safety factor is better with one or two other people.

For what it's worth, most newsworthy incidents involving hikers in my area happen to solo young men who have gotten lost. They are invariably "experienced with the outdoors" yet never have a map, compass, clothes, or extra food & water. I've not kept track, but I can only remember one incident that happened to a group, this being a mother & daughter who ended up staying a night in the woods unprepared.

More rarely I hear about shootings or assaults that happen to hikers, usually solo women or women who didn't stay with their group. I have no idea if being in a group would have saved any of those victims. I tend to think that most attackers aren't looking for a fight, and thus pick easy targets.

Personally, I almost never hike solo because the outdoors is fun & beautiful, and is therefore better when experienced with someone. Hiking alone would be like watching a game or going to a movie by myself: it becomes flat & pointless. And that's coming from a guy who's a bit of a loaner.

On the flip side, take my father: he's an avid Alaskan outdoorsman who once stated "when I die, you'll have to come look for me." He's elderly, yet still tromps around the mountains by himself every weekend. I don't know if he prefers hiking solo, but that's the way he wants to go.