Actually, this para from the petition is worthy of closer investigation, it being the best example of whipping up hysteria with unconnected nonsense that I've ever seen...
Quote traditional marriageIf marriage is redefined, those who believe in traditional marriage will be sidelined. People's careers could be harmed, couples seeking to adopt or foster could be excluded, and schools would inevitably have to teach the new definition to children. If marriage is redefined once, what is to stop it being redefined to allow polygamy?'"
So, in all seriousness...
1. How will "traditional marriage" be sidelined by allowing same sex couples to participate in a procedure defined as "marriage" rather than "civil ceremony", will fewer mixed sex partners perform the marriage ceremony because same sex couples do ?
2. Which people's careers will be harmed, specifically, give one example and I'll give a counter example.
3. Why would couples seeking to foster be excluded, excluded for what, for being married to a same sex partner, or for being in a mixed sex marriage, does this happen at the moment and why will mixed sex marriages make it happen ?
4. What has polygamy got to do with the subject, why introduce it at all, why not suggest that same sex marriage will cause the sky to fall on our heads - its just as relevant and likely.
There's four serious questions to be going on with, I do hope you're prepared to debate your issues.