Yes on both counts.
Since we're addressing the "liberal" camp, the Marxist/leftist viewpoint is that human beings are malleable clay, and that a clever social architect can mold that clay into whatever form desired. Anyone who buys into this viewpoint has got to ignore plenty of evidence to the contrary, and having done so, can then ignore the question of whether legislation is even an appropriate tool for the sculpting. So yes, I think they really "believe" in what they are doing, "belief" used in the religious sense of faith unconcerned with facts.
Now said social engineers need to dress up their ideas well enough to be elected, that's the politics part. (I.e. you have to convince people that they really want to be sculpted.) But if the idea sells, well then, it sells... Quasi-religious socialism is appealing to disconnected urban veal-pen cubicle workers who have no strong existing social or religious ties. They can find some substitute satisfaction in voting for the guy who's "doing good for people" and supporting their causes. I don't think it's just coincidence that the "conservative" Bush-red areas on the election map locate places where people get out of doors once in a while and go hunting and shooting.