Slippery slopes

Sexual morality

If contraception is acceptable, why not same sex marriages? Sterile sex is sterile sex; all that matters is pleasure (hedonism).
If same sex marriages are acceptable, why not polygamy (multiple wives)? It's a natural arrangement in many human cultures (most especially in Islam and Mormonism).
If polygamy is acceptable, why not polandry (multiple husbands)? Some tribes allow this.
If polygamy and polyandry are acceptable, why not polyamorous marriages (any combination agreed to by the partners)? It's all a private matter; the state has no interest in what happens between consenting adults behind closed doors.
If prostitution and swinging are OK, what's wrong with adultery?

If polyamory is acceptable, why not swinging (couples engaging in sex with multiple partners)?

If it is legal for same-sex couples to adopt children, why not same sex marriage?

If abortion is a right, what right do doctors have not to provide abortions?
If abortion is a right, what is wrong with infanticide? Diagnosis of birth defects and murdering the child are both easier once the baby's body is extracted from the mother's body.
If abortion is morally acceptable, what's wrong with breeding babies to provide body parts for adults?
If abortion is morally acceptable, what's wrong with using the unborn human being as a lab rat? What's wrong with running experiments on the unborn, then murdering them in the womb?

If humans have a right to die, then what right do doctors have not to murder them?