My dog is friendly to other dogs 99% of the time - should I stop letting him greet other bc of the 1%?

I've had my dog since he was 10 weeks old and made a point to have him meet other friendly dogs and other people. Now that he's a big guy, I still try to have him greet others we meet on walks. He seems to want to most of the time and whines if he doesn't get to. I ask the other owners first as we approach of course. Unfortunately, this morning, we were approaching another dog and I asked the owner who either didn't hear or just didn't respond, but was smiling and coming towards us. Both dogs were wagging their tails, so it seemed ok. When we got close though, his dog barked and lunged and my dog went NUTS. HE is strong and pulled and lunged and barked. I managed to hold him back and the guy got control of his dog and we moved along. It was very nearly a full blown dog fight. Quite scary. Now I'm wondering if I should keep my dog away from all other dogs. He is 70 pounds and all muscle. I don't want him to hurt other dogs. I don't think this incident was his fault, but I can't tell when he'll be ok with another dog and when he won't. I don't see the signs. He seems to act the same either way up until we get close.

He also had an incident at daycare - got a little defensive of the existing pack in the room and went after a new dog. We don't go to daycare anymore, needless to say!

Should I get him more training? i'm at loss for what to do. He's very inconsistent. Even with people.. he likes 99% of them, wants to greet and sniff them, but then will occasionally bark at someone walking by. Sigh.