I would disagree that a slave has no rights.
Of course we need to establish in what context we are using the word slave. Sex slaves do exist in the modern world and they certain don't have rights, mind you it is normally not consensual. I still maintain that in theory a slave in the bdsm conmtext has no rights but in reality you are right that is not the case. You definition of simply serving 24/7 could include domestics and house servants. Many in the bdsm world use the term loosely just as an office slave doesn't really mean slave or when a dom says the slave is his "property" he doesn't literally mean that.

No contract which asks you to give up that right (or any legal or constitutional rights) would stand up in a court of law.
You are correct of course but I'm not sure what has law got to do with it. When the criminals draw up the robbers contract to determine how the loot is to be split that would not "stand up in court" but it is a contract valid within the criminal world. Incidentally I read that the drawing up of a slaves contract is in itself illegal in Europe.

Compromise is the basis of a good relationship.
Erm not too sure there. Compromise often results in neither being happy. But I know what you mean and take the point. But are bdsm relationships based on compromise? If so, what then does submitting to somebody's will mean if you have negotiated and amended that will through compromise.

As for being ordered to do something you didn't like because the Master/Mistress likes it?
My point was not whethere or not you do it, but whether or not you gain pleasure from doing it because it gives your master/mistress pleasure.

The trick is to find someone who enjoys more of the things you do and less of the things you don't so there is less to put up with.
Yes and this is why many relationships fail. People rush into Vegas style marriages (to take your analagy) before really knowing the person then a week later as they slowly find they don't share the same interests it's a quickie divorce. Makes a mockery out marriage in my view.

And I don't think anyone would disagree with the point about 'I like what you like'.
And as I recall Eddie Murphy in the film tried to be cunning and said "I order you to tell me what you like" but still could not get an answer. He ended up going to New York for his partner and so as it happens did I