As it turns out, Mitt Romney's donations in 2010 and 2011 include a non-trivial gift to several organizations that could be charitably described as viciously anti-gay:
The Human Rights Campaign points out a report by CNN that says Romney's charitable foundation gave at least $35,000 to antigay groups in 2010, with $10,000 going to the Massachusetts Family Institute, which ran radio ads last year warning parents that a transgender civil rights bill could lead to all manner of danger in bathrooms.
One woman said in a radio ad that if the legislation passed (which it did), she wouldn't let her daughter use the restroom alone anymore. And the group's website showed a restroom door with the provocative message, "Who's going to be waiting for your wife and daughter?"
Considering how much LGBT-rights have been mainstreamed, I'm not sure that this won't hurt Romney among Republicans, at least the moderate Republicans most likely to vote for the former Massachusetts governor. That said, this would absolutely be a liability in a general election. More importantly, this should serve as a reminder that Romney-despite his persona-is just as conservative as his competitors, and will govern as such if elected president.
Indeed, odds are good that a President Romney would be more conservative than a President Gingrich or a President Santorum, due to his strained relationship with the conservative movement. Because of the need to build trust with his political base, Romney will have every reason to hew right and accommodate conservative activists. That's not to say that his pragmatic instincts wouldn't be valuable during a crisis, but for the day-to-day business of being president, Romney would be as disastrous as any other conservative choice.