Marriage in our modern world isn’t for reproduction, we’re not living in ancient times. Many straight couples can’t have kids due to fertility issues, don’t see you campaigning against their marriage. Also many same sex couples use surrogates so they do have kids to ‘populate our earth’ and they adopt the abandoned kids and give them a home and loving environment. It is quite obvious for you it’s the fact their gay that your against same sex marriage not because of their inability to reproduce.