Homosexual Marriage Rights- a Possible Slippery Slope?

Recently it was found that Proposition 8 was verified and the ability for homosexual couples to get married in California is now not possible -from a legal aspect. However, there is much debate that is continuing to grow. There have been several appeals that have been made that hold that this (prop. 8) is a violation of civil rights and equal protection under the law. It has been argued that if gay marriages are not approved we will have negated some group of individuals some inherited unalienable right that they possess. I think that the equal protection argument is contained in the civil rights argument, so I will just set my sights on the civil argument for the time being. There is a serious issue here, and I have noticed that, not only from an academic perspective, but also a practical one, when you begin to say, "I am opposed to gay marrages" you are dubbed a Bigot or a "gay hater". I think this is wrong on several grounds, but the proponets of gay "rights" must answer some of my questions if they are to be able to hold that some group X has some type of civil right that some similar group Y cannot have. An example is polygamy. Should we allow polygamy? Many proponets of homosexuality claim that we should not! But why? Is it because there are some set of rights R that are possessed by gays and not heterosexual couples that wish to engage in polygamous relationships? And if so, what are they? Moreover, (here is where it gets slippery) if gays are to get married on the grounds that they have some set of rights similar or the same to those of 'normal' couples then we must be able to logically conclude that those right are such that both X and Y share R, and if that is the case then polygamous couples must also be able to share R, as per they are similar to X and Y. Additionally, if it is a civil and consent issue then why can some person P not marry his or her sibling? It seems that such an act falls under the same R (rights claim). Moreover, what if some animal and some human were to desire union, what would we say then? Perhaps, we would be tempted to say, "no". However, that cannot be right because the same basic claim that some P has and should possess R must hold to some relative extent. Thus, if we allow homosexuals to marry, then there must be concessions given to all the other prior instances listed above. So, I guess we can safely conclude that it can't be a basic human rights violation that we are talking about here, but rather some perverse tolerance claim.

Best,
J.R.P