You suggested I had ‘an attitude’ that, given the context you said it in, is not a good one. You also equated me with idiot owners that ignore lead-on rules, so I’d say you are being fairly unpleasant to me.
An extendable lead would be awful on a path a few feet wide, and they are also horribly dangerous in most situations, liable as they are to snapping or getting tangled. They are also nasty for the dogs as they can’t judge where the lead ends, so if they try to run they get jerked back. Hideous things that I will never use.
No one is suggesting you cut off your nose to spite your face - as has been repeatedly pointed out, there are plenty of open spaces you could frequent, as well as areas where dogs are banned or must be kept on leads. Where stupid owners are flouting these rules, report them.
However, suggest that law abiding owners should be restricting the movements of their dogs in places to accommodate your son is ludicrous.
Taking your suggestion to its logical next step - how wide should the path be before an off lead dog is acceptable? 6 ft? Wider? And how much sight is required? 50ft ahead? My dog likes running around the trees, rather than along the path - is he allowed off lead? Or is that a no as well, because your son might want to play in the fallen logs?
I’m sorry your son is afraid of dogs, it must be awful for him, but it really is your issue to manage - not anyone else’s. You have choices of where to go - many more options than dog owners do.