Also: Where do we stop?
I mean if we have detailed representation bout gender/sexual identifies, how about masochistic dwarves that love pain, legendary masturbator and peeping urist the grand master observer? I would love all these things because it sounds fun to me, but it all might become too tentaclish when Urist McLeatherThong throws a tantrum because of having no chains in his bedroom.
I would think it rather natural to with homosexuality introduce inter-species marriage. Here, Urist. Marry your pet pig, involve yourself in a romance with a kobold swinger's club.
Slippery slope arguments are considered logical fallacies for a reason.
They try to eliminate all distinctions but a single one to create black-and-white contrasts that ignore all middle grounds and argue only extremes exist.
To give an example of why this is such a flawed argument, I need simply make a slippery slope argument in the other direction:
"Clearly, by denying the ability of dwarves to have different kinds of sexualities or relations with one another, you are denying ALL relationships and distinctions of dwarves. WHERE WILL IT STOP?! Obviously, you won't be happy until there are no castes or genders or personalities at all, and dwarves are simply spawned periodically out of the spawning workshop."
Picture this with gratuitous obnoxiously large text if it helps make it seem more ridiculous to you.
Slippery slope arguments like yours ignore the distinctions between one thing and the other. Homosexual dwarves
never have to have sex, so comparing them to masturbation is invalid, as masturbation is
solely about actual sex, and Toady is drawing the line at actual representations of sex, yet not drawing the line at representations of relationships.
Likewise, there is nothing wrong with interracial relations (Toady even says he wants half-elf, half-dwarf hybrids to be possible), but the line gets drawn at sentient beings, for the same reason that beastiality is forbidden in real life - relationships between
two consenting adults are proper, but any non-sentient animal is incapable of consent.
Your entire argument is completely invalid.