Starbucks is stupid for doing this. Truly stupid.
It also opens the door to all sorts of litigation from employees who may been punished for politically incorrect speech.
If no employee can strike up discussions of controversial/political subjects with customers, that is one thing (a hard and fast uniformly applied rule). When the employees are encouraged to confront customers on the highly charged issue of race relations in America (President Obama, Islam in America, police shootings, self defense, amnesty, reparations, white privilege, etc.), they are going to find some employees who don't stick to the script (they don't all tow the liberal line; also, some may be 'provoked' into a hostile response based on something a customer may say).
What good can come of this?