I can see both sides- in FFXI there were often times when I'd be like "Ugh I just want to go out and do x y z by myself". That is part of the reason why I leveled Beastmaster to 85 before I quit; I had so much fun just going out and exploring, beating mobs up and not having to rely on others. If I died then it was through my own stupidity or pushing it a little too close to the wire!

I had other jobs that were for partying, endgame events or helping people out in groups, but with some of the people you come across sometimes you just can't stomach the possibiltiy of encountering stupidity, selfishness or laziness by being in a random group of people you just don't know. Of course not everyone is like that and it is probably unfair for me to put it like that (but I'm sure everyone has come across these type of people at some time or another!), and partying with others and helping random people out is a great way to make friends.

If you want to solo, I don't see the problem with it. Of course there will be things that you will not be able to do just on your own, but if that's good with you or you decide to party with people at that point to get the job done then I see no difference ^^