Partly Cloudy... Or Something

I'm confused. I don't know what's the right thing to do.

Wait... You think normally you do? Don't make me laugh!

Monster made some new friends out walking a while back, as I told you about. We keep running into these dogs and their owner fairly frequently, and we're always invited to greet - and preferably even play.

Hey! Remember me!?

Of course, playing on leash is a bad idea... So the other owner, let's call him Boots, often asks me to let Monster off leash to play. There is a place a little off to the side, where there usually isn't anyone around and I have a fairly clear field of vision to see if anyone's approaching, so I've agreed to this a few times. Monster loves it, as do the other two dogs, and they play and shove and chase sticks and each other...

While I stand there tense wondering if I've done the right thing.

Forget about her, let's go!

I think it's a good thing for Monster to have positive experiences with other dogs. This will help remind him that not all dogs are like Dobie, and make him feel more secure. I'm also not really worried about the safety issue about letting Monster off leash - all his aggression behaviors have only appeared while leashed or behind a fence, and he's never bitten another dog, even in self defense. He is big though, and clumsy. He could hurt someone just by running too fast and not looking where he's going. Although I suppose that's true of most dogs.

But the real problem I'm having, is that this will also make Monster more excited about other dogs! I'm no expert, naturally, but to me Monster appears to have both some fear aggression and quite a bit of barrier frustration. The bit that is fear aggression could perhaps be helped somewhat by meeting other dogs like this, but won't it make the barrier frustration worse? The more he wants to reach other dogs, the more frustration he will build when he can't, right? On the other hand, the fear aggression may be more important, right?

Augh! 

We meet again, my dear!

Boots is very clearly in the camp of "For god's sake, let the dog play! He'll never learn to act normally if you don't let him!", to the point of him repeatedly asking me to come along to a large off leash area for dogs (in the city, with no fence around) and let Monster run free there... I have decided against this, it seems too risky - not just for fear of Monster doing something bad, but something bad could happen to him too - but I remain on the fence about these play dates by the stream (another problem, since Monster can't swim). I feel guilty about not letting Monster "just be a dog", and Boots is pretty impressively good at playing on this guilt.
(Not a complaint against Boots, he simply feels I'm doing it wrong and is trying to help by guilting me into doing the right thing - what he believes is the right thing, that is.)

But guilt is not a good reason for doing something, there should be a clear intention and a plan. Unfortunately I seem to be too stupid to figure out what the frak to do. What is the right choice in this situation? Should he play, or should he train? In one situation I appear to be mean and a Nervous Nelly, in the other I appear to be careless and nonchalant...

Augh! Indeed...

Do I get a vote?