My answer will be written with an audience of wavering or uncertain Republicans, independents, and perhaps some unusually open-minded and moderate Democrats in mind. If you're a fairly committed liberal or progressive, I have nothing in the way of persuasion to offer but this: stop being a committed liberal or progressive.
The Case For Mitt is the Case For Conservatism/Republicanism
Personality politics is what drives many national elections, but it usually massively obscures the fundamental issues at hand. The personality and idiosyncrasies in policy proposals and ideology of presidential candidates is exceedingly more important to consider and weigh during the primary process than it is in a general election. The reason for this is that during the primaries you're winnowing down from a pool of candidates who share many of the same basic values and beliefs, and so the finer distinctions between them become important.
Once we are into the general election, this is no longer the case. We are now dealing with two candidates whose fundamental ideologies are often drastically opposed to each other. And, to get to where they are, each has to have shown some significant level of fealty to the party (and that party's values) which has nominated them for the presidency. Which is a loyalty that usually carries through into their presidency and how they will govern. With this being the case, the real critical distinction isn't between Mitt Romney and Barack Obama but between the Republican party platform -- its values, policies, and vision for the country -- and that of the Democratic party. Mitt Romney is a fairly ordinary Republican; Barack Obama is a fairly ordinary Democrat. What sets them apart as a Democrat from other Democrats or as a Republican from other Republicans is no longer relevant, for the most part.
This is something that many on my own side, myself included, sometimes forget. It is about Obama's failures as a president, sure, but it's important to note that anyone who shares the values of the Democratic party could not have done significantly better because their ideals preclude success.
So, while so much of the national dialogue in the media is focused on things Romney or Obama have said or done, the really savvy voter can mostly short circuit all such considerations by looking at both the Democratic party platform and the Republican party platform. Also helpful would be to compare these platforms to previous platforms and see what direction the parties are headed in. And, in the case of Democrats, taking a look at their attempt to 'remedy' the platform and re-insert some of the language that had been extracted (and shiver).
- If you value the protection of the lives of the unborn (over a woman's "right" to kill), vote Republican.
- If you value the Constitution's vision of a limited government with enumerated powers, and don't think it's a 'living document' (beyond the fact that it can be amended) that can mean anything the prevailing spirit of the times deems it to mean, vote Republican.
- If you value equality of opportunity, self responsibility, and see the dignity of hard work, vote Republican.
- If you think a robust capitalism, with limited constraints, is the best way to organize an economy and lift the conditions of all (and you correctly recognize, contra ubiquitous propaganda to the contrary, that 'too much market' didn't cause the economic crisis of 2008), vote Republican.
- If you believe in fiscal responsibility -- that both individuals and governments should not live beyond their means -- vote Republican
- If you believe in a social safety net for the most helpless in society, but believe that the primary responsibility for them should fall to families, local communities, charities, and local governments, with the federal government playing a very small role, vote Republican.
- If you believe in a strong national defense and peace through strength, but that war should always be a last resort, vote Republican.
- If you believe in choice -- and therefore quality -- in education, vote Republican.
- If you don't believe in socialized medicine -- with its harmful effect on quality and availability of care, and its economic havoc-wreaking -- vote Republican.
- If you believe we should care much more what our allies think about us than about the fickle opinion of the world as a whole, vote Republican.
- If you believe that the entitlement system is broken and unsustainable, and must be addressed so as to bring the debt under control, vote Republican.
- If you believe people should keep the vast majority of the money they make, however much that is, vote Republican.
If you don't broadly agree with these values, then it's my humble submission that you at least abstain from voting, rather than do the unconscionable and vote for Barack Obama.
If I wanted to be really thorough, I would go through those bullet points and argue why you ought to assent to them all, but that is a tall task indeed (in terms of effort and number of words), so I will defer that task to if and when I'm challenged -- in the comments or elsewhere -- on specific points or asked for elaboration.
Sure, it's true that sometimes parties and politicians don't strictly adhere to their expressed ideals and go astray. But by and large, they do sincerely subscribe to the broad values contained in their platforms and will generally govern in the same basic vector of their party. I think this is the case for both Romney and Obama. With that in mind, forget about the men. They are ciphers or icons for ideologies and visions that are diametrically opposed, and should be approached as such.