So glad someone is coming to help you in rl.
Re the muzzle - only use the baskerville muzzles. The dog can drink, eat treats, and be sick, pant if required wearing one. DO Not use the nylon ones ever!
Re dog feeling like he can not fight back -to be honest dogs can give a very nasty muzzle punch if they want to! However I do know what you mean. You must associate the muzzle with good times. The dog must not think - every time I get this muzzle put on I go to places I am uncomfortable in and then I know I will get stressed.
To prevent this I always teach any dog that I have to muzzle or clients dog that has to muzzle the muzzle game. They all learn how to push a football with a muzzle. So once they are used to the muzzle the football comes out and the best game ever takes place. The dog pushes the ball maybe towards a goal, maybe to the owner and gets mega rewards.
The dog then associates the muzzle with fun and relaxation. When you go for a walk the dog may meet a dog but the positive association of the muzzle should hold.
So don't just put the muzzle on to go and walk amongst dogs.
Make the muzzle fun
Some dogs don't mind wearing them at all - some need a while to get used to them. If your dog does you can do the following:-
First thing I would do is hold the muzzle and give him treats
Then I would hold the muzzle and put my fingers through it give him treats (he is not wearing it)
Then I would put treats in the muzzle and he would have to push his nose in to the muzzle to get the treats
Then I would do above and put straps around his head while he is eating the treats
then when he is happy I would have it on for a second and give him the best treats ever and build up from there.
You may not need to through all of that but just in case!
In the meantime teach him to push. Get a post it note and hold it in front of him - he should go to sniff it click and treat, keep doing this until he is happy to touch it with his nose.
Then put the post it note onto a light cupboard door (eg kitchen rather than wardrobe!) he should touch the post it with his nose hold back a little on the click and treat and he will push it a bit harder click and treat.
Practise this and you will get a push. Now put your post it note on a gym ball or on a football and click and treat if he pushes, so not click and treat a bite!
Give a push command.
When he has his muzzle on ask him to push the football and the beginnings of a great game, and a chilled muzzle wearing dog. Also the more tricks a dog learns the more confident they become which also really helps reactive dogs and increases the bond with you. Ok he may be a terror on the streets but at home he is a clever fun dog - it makes it easier to forgive his other behaviour!
All my dogs do the muzzle game if they need a muzzle of not!
Also your earlier comment about what people think - People that matter will acknowledge that you are a brilliant owner who is taking appropriate steps to keep your dog and other people/dogs safe. Others who give a dam 
We all know you are working extremely hard at this and you really should be commended.