I learned an interesting fact.  Illinois was the first state to rescind it’s anti-sodomy law back in 1961.  From there we had a gradual decline until in 2003 where the Supreme Court decision in Lawrence v. Texas ruled anti-sodomy laws unconstitutional.  Then, from that zero point, we quickly see growth in the legality of same-sex marriage and many anti-same-sex marriage laws being struck down by the courts.  I give it ten years tops before we see that graph hit 100%.