Actually... you can!
It was proven by the disbanding of the Jim Crowe laws that enforced segregation on the statement that "you can't make people accept blacks". That was struck down, and ever since society has evened out in the US (except for the backwoods rednecks, but that gets back to Basschicks point about education).
In Canada, gay marriage is legal. If it went to vote in the populace, I guarantee that it would not pass. But this is a human rights issue, not a personal belief issue and the Supreme Court recognized the inherent discrimination of such bans.
It was a kafuffle for all of a month. Now... 5 years later, no one even thinks about it anymore here. It is a non-issue.
Do the religious groups agree with it? No! Does it affect them? No! Are they wasting time daily on this issue? No!
The sky did not fall down. Nothing really changed.
Churches are not forced to marry gay couples (that would also be discriminatory) but they are allowed to if they want to.
You can legisate morality - there may be some short term backlash (as in the 60s when white schools were opened to brave black students), but in the end the issue simply disappears as long as the government is brave enough to let it.
Just my two cents...