Why not a man and a goat?
Ask these questions of any pro-gay marriage supporter, and you'll find out that they indeed have a line, just as you do. They just disagree where the line should be drawn.
They just say to you, “oh that’s ridiculous”.
But that is exactly the initial reaction to gay marriage.
The give away was “LGBT”.
Why did people who were born gay and want rights, include in their movement bisexuals and transgender from the beginning, if it isn’t the “anything goes” movement?
Why would they support bisexuals when that goes against their whole argument of having no choice?
And why include obvious psychological disorders like transgender and men who want to dress up as women?
How is that gay? I guess two men should be allowed to dress as women and both marry as women and be a child’s mother. Why not?
When you ask these questions of a homo-”marriage” supporter,
you’ll usually get “that’s absurd”, and no answer. Also, I’ve had them TRY to turn it around on me and claim that _I_ support interspecies marriage - but, it’s just to divert from actually logically addressing the argument.
When you abandon THE definition, there is NO definition.
When the “definition” they want to propose is arbitrarily based on contemporary societal pressures, they have no standing to say that their definition is more “valid” than the next step they would avoid as “absurd”.