I’m sure glad a protestor cleared that up for me
But lesbians can be monogamous, so lesbians can get married! 
Yeah, that doesn’t violate any constitutional rights at all, at all.
Hey! Now that’s some logic! Here is some more logic:
All mammals are animals.
A carrot is a mammal.
Therefore, carrots are animals.
Yup. Your logic is impeccable.
As is your analogy. 
ETA: on further reflection, your analogy is good, but not impeccable. I can pec it thus: in the OP’s syllogism, both predicates are counter-factual. In your analogy, only one predicate is untrue.
How about
All arguments against gay marriage are logical.
Intolerance is part of Christianity.
Therefore, Jesus wants you to vote against gay marriage.
How about:
Married people need to be monogamous
Monogamy is boring as shit
Profit
Wow, I didn’t know straight people were paragons of monogamy.
I mean, even while homosexual activists were talking about marriage being “heteronormative,” there were swinger clubs.
I suppose you could replace the first premise with something less controversial, e.g.:
- Marriage requires a commitment to monogamy.
- Gays cannot commit to monogamy.
- So gays cannot get married.
That gets around the fact that straight persons are often unfaithful (as commitments can be broken). Note that if true, this argument would imply that a gay man could not marry a woman any more than he could another man — thus undercutting a frequent claim that heterosexual-only marriages aren’t discriminatory.
Unfortunately, in some parts of the world gays can marry. This implies the truth of not-3, which means that we can prove anything we want to. Since this would leave all of mathematics in disarray, gay marriage must be banned immediately.
Sounds like a plan.
OMG! Then Newt Gingrich must be gay!
That reminds me of (IIRC) Jerry Falwell’s argument in favor of capital punishment:
[ul]
[li]Without capital punishment, Jesus would not have been crucified.[/li][li]Without the Crucifixion, there could have been no Resurrection.[/li][li]Therefore, capital punishment is a good thing![/li][/ul]
I never doubted.
Makes sense.
Lesbians can’t be monogamous. Lesbians exist for MFF three-ways.
You talked to gay protesters?
Wait a second! What’s all this about carrots?
The gay couple who lives next door have a pet carrot. They say it does tricks for them but it’s always just lying there whenever I see it.
Carrots are nocturnal mammals.
They aren’t monogamous in any case, have you seen what goes on in a garden? Playing with the sexy bits of other species is just wrong, what are we going to do about inter order tom foolery? They do it outdoors even.
Capt
'es just resting.
Those are just the domesticated hybrid lesbians that you see on film. They are deliberately bred for increased bisexuality and mammary volume. The species varieties of lesbians that are found in the wild can be monogamous. Sorry for the confusion.