Gay Marriage: The Conservative Case (For Votes)

If, as some argue, the Prime Minister were to drop his plans to introduce gay marriage he would be unlikely to win many back on the strength of it. People who oppose gay marriage would remember that he was in favour of it before the going got tough. Those who support it would see that he abandoned the idea in the face of a determined minority. Those who don’t much care either way would notice another flip-flop. In political terms, ditching gay marriage would probably be more likely to put off Joiners and Considerers – whom we need if we are to win a majority – than it would to win back Defectors.
It is notoriously difficult in polling to work out the electoral impact of a given policy with any certainty. People vote for a host of different reasons; their choice must take into account everything they know or feel, good and bad, about a party or candidate. They are therefore very unreliable when it comes to assessing to what extent one issue, taken in isolation, will affect their decision. Some Conservatives will no doubt find themselves unable to vote Tory this time if the plans gothrough – but it is also clear that the traffic would not all be one way...

From a fascinating, detailed article on Conservativehome by Lord Ashcroft, the Conservative Party's chief electoral strategist.
Note its implication that dropping gay marriage has been seriously considered.
And how principle doesn't come into it.