It's not about individual negative experiences (we all had them, more or less), it's about how much LFD takes away from the potential social opportunities that never occur because of it. If grouping would really be such a chore people would be leaving in droves as soon as the novelty of vanilla wore off, but they didn't, even though there was hardly any other content in the game. My other post:
The obliviousness of people to the importance of social interaction (rivalries, friendships, people you look up to, people you want to gank all day every day, ...) is astounding. It's like the fame, the very premise of this game wasn't built on it. The convenience took a lot of this away, it isn't good, it can't be good for a long term survival of the game where player bonding is one of the strongest aspects which keeps people playing and subscribed.