Know the Opposition!
Yes, They Wanted to Screw Us
The real reason why Domestic Partnerships (or in other states, Civil Unions) are not enough, is because our conservative and homophobic opponents really did want to set us back to square one on all legal rights.
This is not widely remembered, but before the petition that became Proposition 8, a previous petition for a constitutional amendment was filed that would have not only banned same-sex marriage but eliminated Domestic Partnership rights. On May 2, 2008, the office of the Secretary of State notified all California County Clerks/Registrars that Initative #1293 had failed to get sufficient signatures to get on the ballot.
The notification of "Failure of Initiative #1293 is right here. Notice who the proponents of that failed initative are; background on them is posted below the letter.

Larry Bowler and Randy Thomasson
On Larry Bowler -- A Republican and former state legislator, and lieutenant sheriff in Sacramento County for 30 years, Bowler is best known for leading the recall effort against State Assemblymember Michael J. Machado; and for authoring Proposition 184 (1994) that created the Three Strikes Law. It would seem he is a narrowly-focused "law and order" type, yet according to Join California, Bowler admitted in a 1996 Los Angeles Times article that he "occasionally carried a concealed semiautomatic .380 handgun onto the Assembly floor during legislative sessions."
On Randy Thomasson -- as read directly from the web site of the "Campaign for Children and Families:
"Randy is also founder and executive director of Campaign for California Families, a statewide lobbying organization. "Leading for family-friendly policies in government and society since 1993, Randy has served as a talk-show host, news director and producer. He holds a bachelor's degree in Radio/TV/Film, with a minor in Broadcast Journalism." Thomasson's credentials are a bachelor's degree in radio/TV/film, yet he freely expresses political views as if he is an expert on public policy. At left is a screen capture from their website, www.savecalifornia.com (!!) which is the "Campaign for Children and Families." [We added red arrows.] Is it hardly concealed that CCF's agenda is to alarm voters, donors and families that their well-being will be taken away or destroyed if lesbian and gay people have civil rights."RANDY THOMASSON is founder and president of Campaign for Children and Families (CCF), a strategic nonprofit, nonpartisan organization standing up for children and families in California and America. One of the most outspoken pro-family leaders on the West Coast, Randy has been on the front lines fighting on behalf of family-friendly values for over a decade. . . . 

To learn more, also see People for the American Way's "right wing watch" here. According to an article in the San Francisco Chronicle, the legal counsel for the "Yes on 8" side, Randy Thomasson and the Campaign for California Families "represents the extreme fringe and is not representative of the coalition that got it passed."
It is clear that Thomasson and his allies wanted to screw us by taking all rights away from us. This doesn't mean that others who backed Proposition 8 are more kind, but they were more realistic. When initiative #1293 sank, Proposition 8 was right behind it with a more restrained (slow) way of doing us as much harm as could be politically expedient.