Why not? Discouraging any other arrangement makes you a bigot. At least that was the common refrain concerning gay marriage.
Mark
That's the same old well worn red herring, slippery slope, and false equivalency equine excrement logical fallacies that I have heard too many times before. . What are you saying- that marrying your underage sister is the same as two unrelated consenting adults getting married who happen to be of the same sex. ?Are you saying that opposing the former example makes you a bigot? That is really just ******* stupid. No one who supports same sex marriage every said that. If someone wants to marry their sister, or two tree people at the same time, or a corps - based on the Obergefell decision, they can pursue in court. It would be fun to see what happens.
It is also a Tu Quoque ,or an appeal to hypocrisy fallacy to imply that someone is a hypocrite for supporting same sex marriage while opposing sibling marriage-or whatever, or just not supporting it
tu quoque (To kwok we )(Latin for "you, too" or "you, also") or the appeal to hypocrisy, is a logical fallacy that attempts to discredit the opponent's position by asserting the opponent's failure to act consistently in accordance with that position; it attempts to show that a criticism or objection applies equally to the person making it. This dismisses someone's point of view based on criticism of the person's inconsistency and not the position presented whereas a person's inconsistency should not discredit the position. Thus, it is a form of the ad hominem argument. To clarify, although the person being attacked might indeed be acting inconsistently or hypocritically, this does not invalidate their argument."