I would never try to argue that going solo is better or worse than going with family or friends. It is different.
I've had so many people ask me how I can have fun when "you don't have anyone to share the trip with or talk to". I have thousands of people with whom to talk and share!!
Of course groups, couples, families, etc. have all the same possibilities for interaction that solo travelers do. What I've noticed though is that when people are there with others, the tendancy is to interact with just their group or family and not so much those around them.
I got into the hot seat at WWTBAM one time while traveling solo. Now I don't claim that it was an original line, as I've since heard others use something similar, but when asked who was there "with me", I looked around at the theater and said "599 of my nearest and dearest friends!"
If you let it, going solo opens up more opportunities for fun much more than it limits them.