I too think it's great, so long as you have your dog under control. My dogs don't like strange dogs, and I hate when people let their dogs run amok and come rushing up to them. They're not nasty, just don't like strangers getting in their faces. I wouldn't like strange people running up to make friends with me all the time either!
"He only wants to say hello" or "Don't worry, he's friendly" are all well and good. Mine don't want to say hello. Pus if I have up to four 40kg dogs on leads with me - I don't want to share other people's dogs either!