I think that everyone has a pretty good reason not to vote for Romney.
In 2004 I held my nose and voted for Kerry.. mostly because he wasn't Bush (the guy I voted for 4 years earlier). After Kerry lost and the initial feeling of disapointment faded, I started to realize that it was actually the best thing that could have happened.
The messes that Bush created in his first four years had only started bubling to the surface. There were no easy solutions to Iraq and Afghanistan, just a choice between terrible and catastrophic. And even though it didn't show, the economy was pretty much already locked into the 08 death spiral. Kerry would have presided over a gigantic mess with a divided partisan congress. Bush may have been incompentent his first four years, but he'd had enough on the job training to do a pretty decent job in the last four years of his presidency. It's hard to imagine Kerry faring a great deal better.
But because Kerry lost, the Democratic party picked up seats in 06, and elected Obama in 08 with large majorities in the house and senate including four months of a supermajority. Without that, we wouldn't have Obamacare. Furthermore, because Bush was worrying about his legacy instead of campaigning, he made apolitical decisions like TARP and the auto bailout that essentially saved the country.
Fast forward to today. The recovery is going to be long and slow because we have major structural issues, too much debt to conduct an effective stimulus, and a workforce that is competing with cheaper and better educated labor in other countries. Morever, there are huge infrastructure issues as well as a global energy shortage that inflates energy prices at the first hint of an economic recovery.
Now, do Republicans really want Romney to be their standard bearer for four years? Do you really think he's going to govern the way he promised in the primaries? Or is he going to go wherever the political winds blow him? Do you think the tea party will tolerate a governing Romney? Elect Romney now and the GOP will lose the house and senate in 2014 as well as many state legislatures. Couple that with the shifting democraphic trends, the difficulty "etch-a-sketching" while your guy is in the oval office, and the eventual rebellion of both the social and libertarian wings of the tea party, and you're left with a shell of a party in 2016 that might never recover.
And that's just domestic policy. Obama has put our country on a pretty good path internationally. Having a middle name like Hussein gives him a lot of lattitude from the international community. (Bush couldn't have gotten away with all of Obama's drone attacks) Compare that to Romney who is painfully awkward and has a tendancy to tick off whoever he's talking to.
Would it not be better to give Obama four more years with a split congress? Even if you think that Romney is better for the economy, do you really think that he's going to be that much better? And after all, isn't that that the real reason why essentially no credible GOP presidential canidates ran this year?
The GOP is much better off letting Obama win now, and using the next four years to moderate some of their positions and conduct EXTENSIVE outreach amoung women and lattinos.