Yeah, you should start leading again by cross-species marriage too. It may sound bizarre now but that's how same sex marriage was a 100 years back. Marrying your pets should be legal too.
They keyword is consent. Animals can't consent. Children can't consent. Having said that, in a few years (decades?), I could see poly-marriages also getting equal standing under the law.
I'm not sure why this keeps coming up in some circles. Is it maybe due to some difficulty accepting that gays are people too?
What benefits would marrying your pet bring? And why marry when you already own?
Maybe I'm ready to start seeing other dogs.