That would be really awesome. But some people are dicks, and on the internet, this shows. Most people don't even consider being nice to each other, to the point of dehumanizing avatars and player characters.
Well, if people can switch servers freely (with limited penalties, as someone above said) the effect a LFD tool has on the community is minimal at best, since that community is fluid to some degree.
And, in Guild Wars 2 a server-only LFD-tool would actually not be a bad idea in my opinion. It helps people create groups, which despite what some are saying, isn't something most people actively do or want to do and since you get grouped with people from your server you can make new (meaningful friends) and will see the same faces from time to time.
I think most people will agree that an automatic tool is a superior idea to a manual channel or something similar for the intents of PuGing (since most people will run with friends and/or guildies when possible), because it's easier to use and doesn't assume someone takes initiative. The only argument against it is the effect on the community, which can easily be solved by making the tool server-only, which is perfectly viable, since there are no rare roles. (E.g. Healers and Tanks)
Edit: This would also fall under the ArenaNet Design philosophy, which prefers actually doing stuff, and not standing around, preparing to do stuff.