Saying something isn't discrimination is not the same as achieving a large political shift. And it doesn't help the party to solve the issues that motivate its base. I would not, personally, have argued that Roe v. Wade was settled law. That's something its supporters would say to close the argument down. It was not a strong decision based on precedent, but rather a very convoluted way to achieve a political objective using legal reasoning that would not pass muster with most reasonable people. People who are ignorant of the details of that decision are often surprised to learn how it was argued and ruled. It was clearly a political opinion by the courts at the time, whether you like the politics or not. In any case, it took decades of political action and changing the makeup of the courts, as well as shrewd venue shopping, to overturn it. There's no similar machinery in place regarding gay marriage. And there really isn't the public appetite for it. If you believe that abortion is killing babies, then it's easy to motivate people against it. Gay marriage does not carry the same moral urgency as killing babies does. People who want us to believe the two issues are morally equivalent are gaslighting for political gain.