When your party nominates a candidate who doesn’t stand for the principles your party supposedly stands for, is it better to support that candidate so that you win an election (sacrificing your principles as a result) or to withhold your support (or even vote for the other party) in order to prevent that “centrist” candidate from discrediting your party with his bad policies?
Is the goal to win elections or is it to advance your ideological goals. It clearly can’t be both, as they usually contradict. Is it better to lose an election or to achieve electoral “victory” that either brings no results or actually moves the country in the other direction (albeit at a slower rate than the other party)? Can anybody seriously claim that winning elections for the sake of winning elections is a sensible goal?