The local dog park is such a great invention! Bringing your dog to a place where they can play with other dogs, sniff new trees, splash in water and get their jitters out is awesome. But it is simply not sufficient as their entire exercise regimen. Since the dog park is packed with very rewarding experiences, it is much more natural for dogs to have access to it as a reward at the end of a long walk rather than in place of their walk.
This is how I like to think of the dog park: it is a place that is full of a myriad of energy levels. Some dogs are more dominant than others, and some dogs have more stamina than others. The dog park will always be a hyper, tense, relaxing or healthy place for dogs depending on the dogs that are currently at the park and how healthy those dogs are physically and psychologically.
It's very common for people to bring their dogs to the dog park without walking them first, so the jitter bug is high, and many times people are unaware that their dog immediately dominates the environment of the dog park once they arrive, making it potentially tense ground when other dogs enter the scene.
I'm not saying that everyone walking their dog before going to the park would solve all of the problems that happen at dog parks, but it would certainly lower the energy level and make for less problems in the long run. The good news is that you don't have to worry about what other dog owners do or don't do with their dogs, all you have to do is focus on your dog and their health.
I believe it is best for your dogs overall health to socialize them after you exercise them. That way they are less likely to overreact in a tense situation, and they have had an opportunity to get in sync with you and your rules on the walk. So take your dog to the dog park, but walk them first!