I really think they can be a good and bad thing, it depends on the individual park and the people and dogs frequenting them.
Personally, Delgado LOVED the dog park. He started at 6 months and did very well, only got into one scuffle and it was entirely not his fault but no damage done so it was ok. Once he hit 9 months though and he was still intact I did notice a big change in the way other dogs reacted to him and that changed the way he reacted to them.
I quit taking him before problems escalated and haven't been back. Once problems start, it's very hard to stop them especially when there's so many factors.
Delgado still loves playing with dogs he knows, so he has playdates with his doggie friends I know and trust and that satisfies that need nicely.
Jasmine - Female Miniature Poodle - born Aug 15, 2010
Loker Delgado Von Stalworth - Male GSD - born Jan 26, 2012
Koda & Zazu - 5 year old male cats
Alex - Male Cocker Spaniel (rescue) - RIP Cuddlebug 2007-2010