Conservative Charles Cooper led the defense, arguing that it is reasonable to fear that allowing same-sex marriage would undermine heterosexual marriage and self-evident that the purpose of marriage was procreating and raising children.
[For the full article, see here.]
The reason that the attorney advocating for Prop. 8 "said he did not need evidence to prove the purpose of marriage" as we currently define it in most states in the U.S. is because there is no such evidence that can be presented! The purpose of marriage, be it heterosexual or same-sex, is to legalize (and solemnize) the committed love between two people, and there is absolutely no reason why heterosexuals should have a monopoly over that institution.
Despite the attorney's assertion, it is not at all "reasonable to fear that allowing same-sex marriage would undermine heterosexual marriage." My wife and I just celebrated our 48th Anniversary yesterday, and I can assure you that same-sex marriage will in no way impact our marriage!
Same-sex couples who wish to make a life-time commitment to one another should have no fewer rights than do my wife and I. Their love is no less valuable or deserving of legitimacy than is the love between my wife and I!
Moreover, it is not at all "self-evident that the purpose of marriage was procreating and raising children," as a lot of heterosexually married couples have no interest in having children and many older people who wish to get married are not able to have children. Yet, we don't prevent these heterosexual couples from getting married!
In sum, there is no rational reason to prevent same-sex marriage, and repeating inanities, and not giving substantial (or any) evidence to prohibit same-sex marriage, shows the level of desperation, and the bankruptcy of the arguments, of those affirming Prop. 8, and also shows the blind prejudice that lies behind the facade of appealing to "tradition" that seeks to affirm Prop. 8.