There's nothing 'the matter' with them. They're protesting against the loss of probably the only true wild part of our City than people can walk through. It's undoubtedly the most beautiful walk in the area and a wonderful place to open your lungs, forget your troubles, and see nature at it's best. It's not just about 'walking the dog', it almost certainly contributes significantly to many people's mental well-being.
The council and NHS has several other options including brownfield sites, but opted for this one as nature can't protest..