I assume this must not be just a matter of principle but of judgment as well. No one wants to let the 2-year-old run out into traffic. Does she have the right to decide to kill herself? To control her own trust fund and invest it in swamp land? Of course we'd never punish a girl for doing those things, but we'd punish adults who helped her carry them out.

It's not obvious what choices a child should be allowed to make. One reasonable source of guidance is to survey 18-year-old women about the choices they were faced with as girls and whether with later insight they feel it was better for them to make the choice or for societal/parental guidance to prevail -- they have no obvious vested interest. Child choice in suicide and trust fund allocation won't pass. I'm pretty sure adult collaboration with 8-year-old sexual activity choice won't either -- I doubt it ever will. They might recognize those few cases of modest benefit of genuine girl interest without subsequent regret and weigh them against the many cases of undue influence from men and an unhappy result.

(I'm glad we at least have two votes for the idea that the supply of 8-year-olds available as sexual partners to pedophiles "come the revolution" may be sharply limited.)