Defeating the establishment is much bigger than Santorum beating Romney (which is highly highly unlikely at this point).
Romney/Obama means that the establishment wins. We get Romneycare or Obamacare.
What does the establishment care which Care they get? Either way they get the lurch to the left that they want.
Maybe you’re willing to settle for Romney but I did that with McCain, and what did that get us? Obama. Every time we nominate the moderate squish, we lose. And then we hear the battle cry to nominate yet another moderate squish because ‘it’s his turn’. And we lose.
America deserves better than a choice between Obama and Romney. Hopefully they get it, but if we quit now, Obama wins.