My personal opinion (not necessarily the official position of the Church) is that the state has a right -- indeed, a responsibility -- to legislate morality in cases where immorality harms others who have not given their meaningful, adult consent to that harm.
So, when we talk about abortion, the matter is clear. From any logical position, including that of honest science, the child is a separate human being with his/her own unique human DNA. As a child, he/she cannot give consent to their being aborted. So the act of aborting the child can and should be prohibited by the state. Government must protect innocent human beings under its jurisdiction.
However, when you talk about other issues like gay 'marriage,' it is more of a gray area. I do not believe it's the state's business who sleeps with whom, provided it's among consenting adults. I agree completely with the Church's position on homosexuality, that the homosexual act is gravely disordered and immoral, but that does not necessarily follow that it's any of the government's business.
Of course, when you bring children into the matter (e.g., adoption by homosexual 'parents') it then becomes a valid area of government restriction, because somebody who cannot give meaningful, adult consent is now involved.
Part of liberty (and free will!) is the freedom to do the wrong thing...if we give government the authority to legislate morality in cases where the innocent is not harmed, it's only a matter of time before they're legislating all kinds of other moral matters and taking away individual liberty. How long before the state's morality police define our moral ideas (e.g., allegiance to the Catholic Church) as the ones that must be suppressed?
So, in other words, while I would love to live in a world that lived by the moral doctrines of the One, Holy, Catholic, and Apostolic Church, I would not want to live in one where all of those doctrines were forced upon an unwilling populace by decree... government should stick to setting basic guidelines to protect individual liberty (e.g., the right to live, freedom of speech and religion, etc.) and leave the rest to the individuals.
God bless you.