If most folks claim they haven't been drunk and done stupid things... they're lying. Luckily, most folks don't do stupid things to or in front of the police.
Once again, I will repeat that the number one tool in the arsenal of law enforcement is the support of the community. Regardless of the technical legal justification for slamming the girl, the image is bad and becomes one more bit of separation from a community that has already partially removed its support from the police.
All the get-what-you-deserve crap completely discards what a police officer is to the community - not just enforcement, but an ideal.
Assaulting law enforcement called to break up a fight you are part of is not “stupid things”. Its assaulting a peace officer.