I have an 18 month old dog who is scared of off-lead dogs, but happy to walk past dogs on the lead or those that are walking slowly with their owners, under close control and even greet those that approach quietly and calmly. The reality is though, that he would most probably prefer not to socialise with other dogs and would be quite happy just having our other dog as his only friend. Other people seem to find this concept impossible to grasp and seem to think their dogs can somehow miraculously make him friendly and sociable. 
In actual fact, he's only scared of off-lead dogs because of the number of times he has had dogs charge up to him and leap all over him. In fact, the first two walks he had when he was allowed down after his vaccinations he was rolled by dogs that did exactly that, having run the length of the park to get to him. Poor pup was absolutely terrified and has never got over it. I couldn't ask either owner to call their dogs back either, because in both cases they were on the other side of the park completely ignoring the chaos their dog was causing.
I'm sure both dogs would be considered extremely friendly towards other dogs, but in reality they were rude bullies with absolutely atrocious social skills.
My lad now starts barking as soon as he sees a dog on the horizon and is constantly anxious and hypervigilant for the possibility of another dog appearing in the distance.
I've done a lot of work with him and had specialist help and support from a number of excellent professionals, but the reality is that he will probably never completely get over it and walks will never be as relaxed as they could have been for us, purely because of the total lack of disregard for others displayed by the other dogs' owners.
I don't understand people's reluctance for their to be a mutual agreement between owners before letting dogs off to play together. It only takes a second to sort out and would eliminate so many problems if everyone did it.