When someone advocates for all adults to have the right to be with any and all consenting adults, or specifically for the rights of polyamorous or consanguineous adult lovers, someone who hasn't bothered to think it through or is being deliberately dishonest might respond with “So, you’re advocating for the abuse of children?”
If this is your response to someone advocating the rights of all CONSENTING ADULTS to be together, something is wrong with your reading comprehension. Adults are not children. Consenting means voluntary, not an abuse situation. Consenting adults being together has nothing to do with abusing children.
Trying, but failing, to avoid looking like ignorant bigots, they might try something like “Yeah but, if we allow polyamorous, polygamous, or plural marriages, or we allow incestuous relationships or marriages, doesn't that make it more likely children will be abused by normalizing it? Isn't the next step moving on to children?”
This is an attempt at guilt by false association. It is something LGBTQ+ people have been dealing with forever. “If you allow gay people to be together, it will make it easier to molest children!” It simply doesn’t follow. It’s a lie that most LGBTQ+ people want to abuse children, and it is likewise a lie that people who are ethically nonmonogamous or consanguinamorous want to abuse children. Child abusers are going to try to abuse children. Children will be more likely to be abused and to keep quiet about it the more taboo we keep sex in general.
There are places where consanguinamorous relationships between adults are not criminalized, including a couple of US states. This has not caused an increase in child abuse in these places.
When it comes to ethical nonmonogamy, citing a few isolated villages or compounds where women don’t have equal rights and children are treated as property as proof it leads to child abuse is dishonest. Children are abused by professing monogamists every day, while most parents involved in ethical, disclosed, or consensual nonmonogamy are great parents who are not abusing children in any way.
Keeping unjust discrimination in place is wasting resources vitally needed to prevent and stop actual abuse. It makes it less likely victims and witnesses of abuse will cooperate with authorities if their own relationships are criminalized. Every bit of time and money wasted on trying to stop consenting adults from being together how they mutually agree is time and money that isn’t being spent to help people who are actually being abused.
There is no good reason to deny consenting adults their rights to be together how they mutually agree.