The disadvantages of being alone are more than its advantages. Even though i prefer to stay alone most of the time, but surely not all the time.
When you be alone you can be more free and do whatever you want, but being alone makes people less sociable, and it may lead to anxiety,depression, suicide, drug addiction, and alcohol addiction. But if someone chooses to be alone it can be experienced as positive,and pleasurable.
By the way i think that internet makes most of people like to be alone than before :S ....