[on parent-child incest]
Power differentials in consanguineous sexual relationships do not provide a good reason to deny the rights of lovers to be in these relationships and to marry, if that is what they want. The power differential allegation applies least of all to siblings or cousins who are close in age, but even where the power differential exists, it is not a justification for denying this freedom to marry.
There is a power differential in just about any relationship, sometimes an enormous power differential. One person is more emotionally needy than another. One earns more than the other. One is more educated than another. One has more friends and family than another. One has more life experience than another. On and on it goes. A 21-year-old woman can consent to group sex with three 40-year-old cage fighters she just met, or sex with an older man who boarded in her family home for most of her life, or the President, or a married billionaire sultan, but not her half-brother or her genetic father who she first met a year ago and has been falling in love with? To question if consent is truly possible in consanguineous relationships is insulting and demeaning. If someone her age can consent to join the military, operate heavy machinery, or be sentenced to life in prison or even to death for their actions, how can we say she can't consent to love another adult the way she wants?
There are sober, functional, healthy adults who consent to consanguineous sex with an older relative, and many of them want to marry. It shouldn’t be illegal or questioned, unless you would do the same to any intergenerational relationship between adults.