This actually sounds pretty much right for once.

Cops should be reminding people what the law is and assisting them with following it.  They are in no way obligated to pay for people's taxi rides.  But they can, for instance, remind people - via their presence -  to get a taxi instead of driving, help people call rides if needed, make sure the really really drunk are headed in the right direction, etc.  That actually sounds like a solid community outreach opportunity.  And while they're there at the bar openly they are probably also cutting down on the chance of anyone being sexually assaulted, any general fights breaking out, any theft going on, and a host of other problems at the time as well.

The flip side of that coin is that any cop 'bar sitting' as it was called up-thread by CruiserTwelve and making zero good faith effort to prevent DUIs from starting should be criminally liable as an accomplice.  The same way that many states are now charging people who let a drunk friend borrow their car with a crime.  The cop in that situation has the authority and the ability to prevent that crime from occurring, the knowledge it is occurring, and makes no effort to prevent it before it begins.

Does anyone remember back when it was the police's duty to prevent crime from happening and not just document the results of crime after it impacted people's lives?  we should get back to those days.  this seems like a good move in that direction.