A lot of the heroics are doable solo, it just takes a lot more patience and time. To the point it would be far faster to get a friend.
Bounter Hunter's have it easier cause their very first companion is a healer, the best one to have when soloing.

However as much as I like the Old Republics story telling, it was big design problems. It requires you to grind you essentially everything so you're at a level to keep up with the story fights. Working with players offers about no benefit other than social points and speeding things faster, they could use a system that makes it actually more engaging. :/

Though an MMO is always hugely reliant on the communtiy, a good communtiy lets it flourish. A nasty one will cause it to die because socialness is essentially needed to do a lot of the stuff in the game.