...i admire you for wanting to respond respectfully, which is not something many would do (including me, id be a tad bit *alot* rude)
simply tell him that his opinion is just that! it is HIS OPINION.
Assuming you live in the United States, tell him about your freedom to speech, you are not harming him in anyway...and if he feels that this topic will make him mad, then he can quit corresponding..his loss...But you are not about to conform to his opinion that equal rights is not up for discussion...Because it is..it is a BIG deal in todays society.
okay that was nice me.
a@@hole me would mainly consider saying:
tell that ignorant a@@ bigot to stfu!