They do not have the freedom of choice to marry or not like the rest of the population.
...or more accurately, what prop 8 does is to strip them of that ability to marry that the rest of the population enjoys.
"Freedom of Choice" that was the term I was waiting of you to use in the way you did just there.
When it comes to freedom of choice, there is only one law in the U.S. that this applies to so adamantly...abortion. Now it shouldn't take a rocket scientist to figure out that I am pro life, but I'll use this arguement to back my point.
The idea with freedom of choice when it comes to abortion, the idea here is a woman becomes pregnant, she is now faced with something she cannot control, that baby is in there whether she likes it or not...no matter what she is pregnant.
Yes, the arguement can be made and should be made that in most cases she chose to have sex and take that risk, but it was an arguement that was left out of the majority when this law passed.
Now, based on this arguement, things that are out of our control should not be subject to violations of freedom of choice, if you're pregnant you have the right to choose what you do with it. Same as when it come to race, this is something that is out of your control.
Being homosexual, this is deemed purely a choice, all medical evidence points no where else, there is no genetic factor and this is what most have recognized. So in turn, there is no violation of freedom of choice when it comes to gay marriage, they made the choice to be gay.
Now, you could easily argue that there is something in the constitution that protects freedom of choice on something that is a personal choice and not beyond control...religion, this is a fact, it is protected in this manner. However the institution of religion is protected in this manner due to the view of it's importance to society as a whole and functioning society. The right of gay marriage would have no such effect and neither does denying it have the adverse effect.
I'm sure at some point, the gay marriage issue will reach the Supreme Court, when that time comes the constitution may add a new amendment...we'll see. Of course as Justice Sutherland once said, just because a decision was made by the court, does not mean it was the right decision. This phrase has been used by the dissenting minority ever since. (BTW, don't quote me on it being justice Sutherland, I'm almost positive it was he who said it but I may be remembering incorrectly.)
Then of course there is the notion of "The Right to Privacy" something the court held on to when making abortion legal, even though the very idea and wording is unconstitutional in this manner...something that almost every judge since has acknowledged, even ones who support abortion. So using that as an arguement would be a stretch, simply because it was made an exception when it came to abortion and has rarely been used again, actually I can't think of any major cases since.
The Right to Privacy only applies to things such as:
1. making known a plaintiff's identity for the defendant's benefit
2. placing a plaintiff in an damaging or dangerous position in the public eye of perception
3. publicly disclosing private facts about the plaintiff
4. unethically intruding upon the seclusion or solitude of the plaintiff
These were the original measures taken, later to be added would be such issues as health and certain financial matters, communication and the home.
So yes, the right to privacy would protect a homosexuals privacy concerning what they do in their home, but the right to privacy gives no inclination to protect against denying gay marriage. There is no where to fit it in there with what we have now, which is why only a constitutional amendment could change this.
Last thing, be gay, don't be gay, I don't care either way. Do I think it's wrong and immoral? Yes, but it is not up to me to judge others actions, but it doesn't mean someones actions that are a personal choice and by no means thrust upon them, should be thrust on me in a manner that damages things I hold as a sanctity.