Just remember there are good and bad in all breeds and all races of people. Your fear is your fear, only you can make the judgement of whether your fear is correctly placed or not. It really comes down to the owner and how the animal is socialized or treated. I have had a Rottie in the past and he was a gentle loving dog, I have been chased by a pack of nasty Chihuahua's in my youth. Just as another reminder that it is the people and not the breed - do you remember the story of the French woman that had her face chewed off by her dog. If not her dog was a Labrador Retriever, how many vicious Labs have you run across?
For the most part, agreed. The question I have is really more about the fact that there is no way for me (at the park with my kids) to know if you (at the park with your Rottie) is one of the good guys or not.
It just seems a little thoughtless to me that owners of such dogs would bring them to a place loaded with kids, making nervous wrecks out of the parents. (fully recognizing my own shortcomings as an arguably hyper parent).