We have a (dog) reactive dog. The only pubs we go in are ones where we know the layout, tables are spaced far apart and we can keep out of everyone's way, and there is more than one way in or out. We never stay for more than an hour. It's like being in the SAS sometimes! If we walk in and its busy, or there are other dogs that look like they want to be friendly / may approach then we leave immediately. I do expect other owners to be respectful and keep their dogs away from us as far as possible, but I fully recognise that Ddogs issues are our problem to manage, and we never want to put her in a situation where she feels uncomfortable and might react anyway. She's happy enough in a quiet pub with other dogs minding their own business at other tables, but can't cope with any more than that.
We've only ever had 2 'incidents', one in a pub garden where we were sat in a corner close to the exit and there was a sign saying dogs must be on leads and someone came in with an off lead spaniel that came bounding over, and once in a pub which was totally empty, until a couple arrived with a labrador and for some stupid reason decided to sit right next to us even though we explained the situation and asked them not to, they wouldn't even wait a few minutes for us to move to a different table because they wanted to sit down at the specific one next to us so badly. Their dog was off lead and approached ddog who was backed into a corner under the table, up until that point she'd been happily enjoying her chew by our feet.
So in short, I think the owner obviously has a responsibility to keep their dog under control and try to avoid situations where the dog will react, but as a reactive dog owner, which is hard and fucking soul destroying sometimes, its always hugely appreciated when other people recognise the situation and do their best not to let their dogs approach and make it worse. Sometimes in a tricky situation all you need is a minute or two to gather up your dog and skedaddle, but lot of people don't even give you that.