Got to agree with Bullbreeds and Sallyanne.
I get abuse when my dog is on the leash and is approached by a loose dog if the outcome has not been friendly, apparently its my fault for having a dangerous dog.
If he were off the leash

I dread to think.
I am quite fortunately if the other dog is friendly Duke will play if not Duke will roll his sleeves up. I won't compromise his safety nor mine by letting him off the leash to greet unknown dogs.
If you can hand on heart say your dog off leash will not approach a dog on a leash then thats fine.
Sue