Your dog and you are not exempt from the existing law that says you can't walk your dog with a leash.
Whether it's old, or young, or well-trained, or sweet-natured, or unbelievably adorable, or you think it's unlike Other Dogs; Or if he or she has a disability unrelated to leashing, or is a super-expensive designer dog, or (as you claim because you're apparently psychic) "would never hurt anyone." Or whether you think you're a special snowflake.
The law says you must have it on a leash.
It's not my responsibility as a citizen of this city to beg you to comply, or to mount a convincing argument about of the importance and rationality of leash laws, or to listen to your reasons for ignoring the law, or to explain how your dog's running freely affects my dog.
The law says you must leash your dog. Whether you like it or not.