Ok, here goes again.
I do walk my girls when they are in season, I see no reason why I shouldn't unless it is obvious that they are at the difficult time. I do also have an entire dog so I am well aware the effect this can have on him (Penny is in a permanent oestrus state atm which we have been dealing with for 8 weeks now). But I do have friends with entire dogs and I wouldn't mix the two. If one of my girls is in season then they will be left behind and I walk them separately later on. I also tend to walk in quieter areas where I know less people choose to walk there dogs. I let them off lead but am so careful to keep checking on whats around me and I always call them back if I see any dog. I always shout to the owner too from a safe distance that I have an in season girl with me.
I've also met dogs who know when my girls are coming in, even before I did. So Lab owner may be right that as far as he is concerned he hasn't seen any signs, but I would never let the situation get out of hand, I would have presumed the dog knew something I didn't and would have left the walk. (dogs can predict a girl coming in season sometimes up to a month before it happens. Penny actually came in to season on that occasion the day after and apparently this dog had been used at stud a couple of times previously.)