MMOs are NOT single player experiences. If you go through an MMO and just keep to yourself, you may as well have gone out and bought a normal RPG because you'll get more of an experience engineered to your tastes.
When I first got into SWG I started with some of my friends. We didn't always play at the same times and such but we ended up finding a home on Corellia, kept seeing the same people fighting with Imps, helped them out a few times, started talking and eventually joined their guild. I got even more of an experience out of it with the guild members. Everyone was nice, we'd joined a pretty solid group of players. It was very Utopian. I didn't even really focus on leveling to be honest, it was just an enjoyable experience.
With WoW I joined after it had an established player base, but I joined with a good friend of mine again. We'd go hit up dungeons etc together. But really the focus is always around the people.
If you get buried in being a completionist, you may not find the experience all that gratifying. But if you get buried in relationships it makes everything work well.
Yeah you can play normal RPGs online with friends and they are great experiences, but you don't have the flexibility of an MMO.