Christian right
Many members of the Christian right believe that the Bible says it is bad to be homosexual (gay or lesbian). They used to support sodomy laws. Today, they are mostly against allowing gay marriage. They have had many laws and initiatives passed to stop gay people from marrying (such as California's Proposition 8). Some of these were found to be unconstitutional in the courts. To make stopping gay marriage constitutional, many have pushed for an amendment to the United States constitution to ban gay marriage.