It is YOUR responsibility to keep YOUR dogs under control and NOT to interfere with others. Everyone has a right to walk undisturbed and unmolested by other people, children and dogs.
If the positions were reversed how would you feel?
The dogs on the lead are restrained for a purpose:
the owners would like to extend the same good manners to others they would expect from others
the owners only want their dogs to interact with others on the owners terms
the owners may have convalescing/invalid dogs
the owners may have rescue dogs they are rehabilitating
the owners may have dogs that are anti social and are kept on a lead to prevent injnury to yours
It matters little why others choose to have theirs on leads and "he only wants to play" is the bane of a lot of dog walkers lives when a) it is generally used as an excuse for bad manners or poor control and b) when they are trying their best to keep their dogs out of trouble etc.
You say your dogs have done really well in training classes

well that is all fine and dandy but until and unless they "do really well" outside they are obviously not adequately trained as it "goes out the window", ergo they are not "trained".
Suppose the dogs they wanted to play with were on the other side of a busy road?
I am sure many other people do not enjoy walking their dogs as much either if they are going to be bothered by two out of control dogs...............
obviously occasionally the odd slip up happens but when it is a daily occurrence it can get more than a little wearing to some of us.........