No parking

My school is on a busy street, so parking is difficult. Up until a few months ago we could park in our parking lot which was great if you got there early enough to get one of the spots. The later you came to school, the less of a chance you would get one. Some people took that to mean the later you come the more creative you should get with parking in the lot. The intercom would announce throughout the day that a car needs to be moved because it's blocking someone. Leaving on time was out of the question because your car was buried behind four cars blocking you in. It was frustrating and the principal tried to fix it, but nothing worked.
Finally the fire department came in and saw how we were violating the building codes, so they fined the principal and declared the parking lot off-limits. So now no one can park there anymore. Another case of a handful of people ruining it for everyone.
It reminds me of the dynamic in my classroom. I sometimes punish the whole class because of the behavior of a few people. I feel bad about it, but at that moment I feel it's my only choice. My principal couldn't find a good solution in that situation and sometimes I can't either.
So now when I'm walking three blocks from school to where I'm parked, I try to focus on all the great exercise I'm getting.