I would never dive with someone I didn't know, and as a solo traveler, am rarely with anyone I know anyway. Being a photographer, I really have no time to keep close track if another diver. I sometimes dive with a guide, and he's supposed to keep track of me, not the other way around. If he gets "lost", not a problem. I'll see him on the boat.
I know that the person most interested in keeping me safe is myself, so I've developed the mindset of being self reliant. I think that makes one more aware of the environment and the potential dangers, thus planning accordingly.
I once had a buddy that got into a bad situation when I had about 50 dives. In trying to help her, I got caught up in it as well, and we both had to be rescued. Having a buddy does not necessarily make things better.
When I travel/dive, I encounter quite a few others traveling alone. Invariably, the ones with experience will dive solo.