Totally understand how you feel. We have a dog reactive Samoyed, who is about 10. We got her when she was 3 and we are her 6th home, according to the rescue centre. She reacts aggressively when she sees another dog, which we think is a fear reaction. We have another Samoyed, male, also about 10, also rescued, who picks up on her stress and then sometimes behaves as if he is also reactive. She snapped at him the first time they met but was then OK because he backed off.
She has changed our lives, and I often think of the 'good old days' with previous dogs, when we could go to a pub or cafe with the dogs but without the stress. We have taken her into pubs and cafes but have to check them out first to see if there are dogs inside, in which case we don't go in, and sometimes have had to leave mid meal, if other dogs come in and she gets too stressed. Can't remember how we found this out, but if she's kicking off and getting stressed, she instantly calms if DH picks her up and carries her out. Not easy, as she weighs 25kg, but it does amuse the other customers and sometimes it's the only way to get her safely out of that situation.
She has calmed down a lot during the 7 years we've had her but we can never completely relax when we take her out. She can get on OK with other dogs if they are introduced in the right way and now has several local doggie friends that we go for walks with. We find that she still reacts initially in the same way, snapping, lunging, growling, but calms down afterwards much more quickly.
She's the most difficult dog we've ever had in 30 years of having dogs but she's great at home and with people and her issues are caused by whatever was done to her before we got her, not least being rehomed so many times and probably being attacked, we think. We amend our lifestyle to accommodate her needs and if that means we can't go to some places and do some things then so be it.
We've never managed to get her to accept wearing a muzzle, she will scratch her face open to get it off, so we gave up on that. We consulted a behaviourist when we first got her but didn't find it very much help. She's never been off lead except in a secure field, which I feel is so sad, but we can't take a chance that she will hurt another dog. I too get annoyed with the 'it's OK, my dog is friendly' brigade who can't control their off lead dogs, but I have to remind myself that I used to be like that. We've learned a huge amount about dog behaviour and how to manage it as a result of having our girl, it makes life interesting.