I'm not sure that would be much of a victory when the result is a nominee who no conservative would have found at all acceptable before the process began and only become marginally acceptable by default.
If Romney gets the nomination and is creamed in the general election (which is very possible), the pundits are going to say, "see, a conservative can't win" despite the fact that Romney is no conservative. If Romney does get elected, we get stuck with the most liberal Republican our party has ever nominated. By accepting Romney as a conservative, we are allowing the Rockefeller Wing of the Republican Party to infiltrate the conservative movement.
Once again you’re comparing Romney’s worst case scenario to some perfect candidate’s best case scenario.
Of course there is some risk with Romney, and of course there is a down side.
But McCain IS Romany’s worst case scenario, with no upside.