Girl, you are preaching to the choir....I have a handful of dog park related tales on here that I've written. Bottom line, the dogs are generally fine, the people are fucked in the head.
Why is a big dog in with small dogs? At our park, they have 2 distinct sections, one for under 40 pounds, one for under.
Some people are great. Others, not so much. I've encountered so many irresponsible owners, it'd make your head spin, from aggressive dog owners to just plain lunatics. Luckily, I have a big mouth and a law degree and have made it well known...they watch their step around me for some reason. ;)