It seems like there are two things to point out here...
1) I suppose it depends on the severity of the craziness. If it's dangerous or life threatening then it would be beneficial to get the hell up and leave. As for the just plain stupid things like being loud, obnoxious, rude, degrading... I'd stay just to either make sure they got it in the end or so I could tell my friends about the idiot I accidentally went on a date with. :p
2) People probably don't have the gall to just get up and walk away or they may be afraid to! Some people honestly tie the craziness to violence and just decide to hope for the best if they comply with the nutjob. This is stupid. Other people are being polite and deciding to end things peacefully.
Honestly, from my point of view... just get up and walk off. If anything seriously crazy goes down then there's always someone you could call to help(i.e. friends, police, etc). I believe pepper spray and brass knuckles are good investments.