Also, I wouldn't say the police are 'hands off' - to the contrary, I think the SFPD do a great job in serving their highest purpose: public safety. That's safety for everyone, and even with the mass of numbers, cyclists remain far more vulnerable than admittedly disenfranchised cars stuck in the mass. [I am particular sympathetic of the taxi drivers who are losing a night's income]

I'd add that in my experience, there is an unfortunate "testosterone brigade" who enjoy the confrontation - but the onus then is on everyone else in the Mass to counter them, to remind them that a friendly wave and a smile is their best weapon. I can count the confrontation events I've witnessed on one hand, I can't begin to count all the times I've seen mutual appreciation, public support, and solidarity.