Elnia from the Pink Pigtail Inn has an interesting post comparing the Dungeon Finder tool to pornography: From "unshackling sex from intimacy is the core of the porn industry" he/she [sorry, men with female avatars make for ugly grammar] concludes that grouping with strangers in WoW is the equivalent of fucking strangers in porn. Now I'm not disputing that sex with intimacy is better than sex without intimacy, but does that really tell us anything about how grouping in a MMO should be?
Personally I do prefer groups with guild mates to groups with strangers, and I think most people do. I'm nowhere near getting the achievement and the dog from the Dungeon Finder, because my level 80 characters use it mostly to run guild groups, which doesn't count for that achievement. My characters not yet at the level cap on the other hand group with strangers all the time (not getting the achievement either, because only heroics count for that). So am I a social or an anti-social player?
The answer of course is that I am social if I can. What you need to consider is what the alternatives are. For my level 80 characters the alternatives are between grouping with friends or grouping with strangers, and I choose the more social option of grouping with friends. But for the lower level characters the problem in nearly any guild is that it is unlikely to find enough players of the same level online. Thus the choice is between grouping with strangers and not grouping at all. So grouping with strangers is still the more social option.
And then of course many people do not want to engage in too intimate social relationships over the internet. Sorry to burst your bubble, but the relationship to your guild mates is not equivalent to your relationship with your real life friends or your significant other. In most cases you know nothing about your online "friends", beyond that they share one common interest with you, which can be as narrow as the common interest in beating the next raid boss. If you took a successful raid of 25 people and got all those players together in the real world to have a beer, the meeting would be rather awkward, because they would find that the group consists of people of different age groups, education, and social classes, and there wouldn't be much besides WoW to talk about as common interest. So why would grouping with near-strangers with a common guild tag be so much better than grouping with complete strangers?
You simply cannot force intimacy. The big social revolution of the Dungeon Finder is to enable you to group with strangers, because it was found that the alternative was much worse: Only few players joined really social guilds, while many other people were either forced to solo, or to engage in fake intimacy to get into a guild and thus into a group. To use Elnia's sexual analogy, the alternative often was not real sexual intimacy, but the one-night stand, in which someone (or both) pretend love to get the sex they really want. Needing a guild to find a group was actually bad for social relationships, because it ended up with phenomena like guild hopping, or guilds inviting people based on their character class and gear instead of on a set of common values.
World of Warcraft with the Dungeon Finder is a *more* social game than without it. A quick dungeon run in which you said either nothing, or just "hi" at the start and "thanks, bye" at the end is still more social than spending that time soloing. And not all Dungeon Finder groups are like that, for example I found it breaks the ice to put a fish feast on the floor at the start and invite everyone to get the food buff. And once in a while you will be grouped with people from your own server, and end up putting each other on your friends list. And that is the best a tool like the Dungeon Finder can possibly do. Because if you were only allowed to group with people you already had a beer with, we'd all be playing solo all the time.