I really don't see how this feature would ruin the community. The idea is that if someone behaves poorly in a group run that you can warn others, and eventually cause them to either change their ways or be unable to group. This system simply does not work. Sure, if someone is a jerk when they group with me I might not ever play with them again, but odds are other people are going to group with that person no matter what I say (and I don't see why other people should automatically take my side to begin with).
I like the idea of a LFG tool for 2 main reasons.
1. Forming groups as they are now, time required is a wildly inconsistent variable. If I only have 2 hours to play, it's hard to say if that's enough time to run a FP, particularly at mid-levels where there are fewer players looking for the same FP's. A LFG tool would allow me (hopefully) to see approximately how long is needed to form a group. Perhaps even more importantly, if I have to leave the queue due to time, it's much less of a hardship on the people I'm in the queue with than if I were to have a group of 2 others and have to bail on them before we got a 4th.
2. I like the cooperation of playing with other people, and the idea of taking down opponents I wouldn't be able to otherwise. That said, I'm not looking to make friends in this (or any other) game. I'm not the kind of person who will log into a game just to socialize. Being able to get a group of random people together to accomplish 1 clear objective, then disbanding and likely never seeing those people again works great for me.
tl;dr
A LFG tool would be great for people with limited time or who just don't want to get extracurricular with the social aspect. I would prefer a system that tries to match players with others from their server first, but I think a LFG tool is much needed.