Legal Question in Constitutional Law in California

First off you are obviously confused about how proposition elections work. If 7 million voters had voted AGAINST Prop 8, there would be no law to overturn. A proposition only becomes law when a majority votes FOR it. More importantly though, I think you need to go find your high school social studies teacher and tell them that they are a complete and utter failure, because you are clearly completely ignorant about the very fundamental principals of our country and its government. We live in a federal constitutional democracy. That means we have two constitutions governing every state, the state constitution and the national constitution. The states are free to put anything they want in their constitutions, but only if it is not unconstitutional under the national constitution. Among other things this means that the voters of a state cannot put something in their constitution that takes away rights that people have under the national constitution. The national constitution says nothing about marriage, so the states are free to put things in their constitutions about marriage, BUT the national constitution also contains an equal protection clause. Prop 8 has been found by the court to have put things in the California Constitution that violate the equal protection rights of same-sex couples. Therefore the court found Prop 8 unconstitutional. That decision is, however, under appeal to the federal appeals court. Whichever way that court rules, it is almost certain that the decision will then go to the U.S. Supreme Court which has the final say on what is and is not allowed under the national constitution. So stand by for further developments.

Because it was found to violate the U.S. Constitution. No law can do that, no matter how popular it might be. If, say, the entire state voted to outlaw Judaism, the law would be struck down because it violated the guarantee of free exercise of religion. Prop 8 was struck down because it violated the guarantee of equal protection of the law.