My pointisn't that games should ever force you to group. I said I enjoy games that promote community interaction. There is more to interacting with other players than just group quests and raids but most MMO's don't seem to have that figured out.
What about Rift for example as a way to promote community interaction? There are 2 things that spring to mind immediately (I've been playing for a couple weeks now and am level 26):
1) Public Groups - you can set yourself as able to be grouped with at any time. When Rifts spawn in the world and multiple random people converge on the Rift to fight it, you get the option at the top of your screen to join the Public Group, thus creating some interaction and teamwork in order to seal the Rift. Also, there are often zone-wide events that happen where large-scale invasions with dozens of Rifts and Footholds will appear in the zone along with boss-level mobs to be fought off - these are great fun.
2) Instant Adventure - queue up for one and join some random people in completing missions across the zone - these are also fun and provide excellent rewards. In addition, you can often get the help of these random people in completing the quests you already have because these instant adventure quests often involve killing the same mobs you need to kill for your solo quests. Plus, these are very quick - I did a series of 2 instant adventures in a row (again, very low barrier to entry - complete the last adventure in the series and get an option to Teleport straight back to a starting area for a new series, and they are different, not the same repeating quests) and it took me about 30-45 minutes to do.
I think where Rift has succeeded is that the barrier to group play is so low that it doesn't make sense not to do it. I generally prefer to level solo and then group at end-game to experience the end-game content. However, I find myself a part of multiple groups every time I play because of these random encounters that happen. There are also great incentives to grouping in the rewards that are available - Rifts are multistage, the later stages are timed, and if you are appropriate level, it's very difficult to beat the timer, which opens up additional bonus stages that increase the rewards, which is a great incentive to group.
I don't disagree that there are other ways to promote community interaction bar grouping, but I think Rift has succeeded in the more traditional "community interaction" of grouping with their no-friction public grouping and providing world events that encourage it and reward it.
That being said, I do agree that SWTOR has failed in this regard. A trip to the official forums is painful with the amount of hate, venom and general douchebaggery that is on display there. And the in-game community in some cases is almost as bad.