John Piper puts it best:
No endorsement of any single issue qualifies a person to hold public office. Being pro-life does not make a person a good governor, mayor, or president. But there are numerous single issues that disqualify a person from public office. For example, any candidate who endorsed bribery as a form of government efficiency would be disqualified, no matter what his party or platform was. Or a person who endorsed corporate fraud (say under $50 million) would be disqualified no matter what else he endorsed. Or a person who said that no black people could hold office—on that single issue alone he would be unfit for office. Or a person who said that rape is only a misdemeanor—that single issue would end his political career. These examples could go on and on. Everybody knows a single issue that for them would disqualify a candidate for office.
Read the whole thing.