Yes people do keep fish on their own for different reasons (though mainly its because the tank is too small to allow tankmates).
My attitude was until recently that there isn't anything wrong with keeping cichlids on their own, then I read a thread on another forum and it changed my outlook. The thread was about 'glass banging' cichlids and if its stress or something else that causes it.
What I got out of it though was that I won't keep fish alone anymore, they need some interaction I think.
I witnessed this when I first started my 90G, I put in my severum first and 2 polypterus, the severum would glassbang my finger if I got close, now with my oscar in there with the sev it no longer glass bangs and I have to say its colours have improved. I also like the way they sometimes swim together and if the oscar picks something up from the bottom, the severum shoots over to check it out. Thats gotta be providing more stimulus. I also would never keep a fish in a bare tank, all my tanks are decorated as I also believe this gives the fish something to do or atleast look at. My severum also hates plants of any kind, but I still buy and put plants in his tank just because it gives him something extra to think about and do.
I suppose the big question is what fish are you thinking of getting and the size of the tank. Cichlids are a big group of fish and I should think you could have some form of tankmates with the majority of them.