although I myself don't have harbor any interest in my sibling or cousins to say , I do not think that incest is particularly bad or unacceptable. If you happen to see your brother/sister romantically and so do they then being in a relationship is by no means wrong, if you love them ,then it is so. Considering the biological issues , if you truly are in love and want to be together then accepting the burden and responsibilty it brings with it is inevitable , get it straight you can't have kids but being in a sexual relation is not wrong in any way, sex is more than just reproduction for humans , it is the embodiment of love or lust or both (you can always adopt a child). Like fuck man , if you truly are in love then being together is your right no one can deny.
Regarding emotional and psychological factors , it happens to the weak hearted , as I said earlier that you need to accept the consequences it brings forth , there are times when have to choose , maybe your families will hate you but you need to weigh whether being together brings you more happiness or sorrow , even in normal love many couples have to make a choice between family and lover sometimes , some run away to different cities and even countries to mention, if being with a person brings you happiness I don't see any fault in that .
This is very much like being opposed to same-gender relationships. You have no idea how the concerned party feels so don't go on spewing shit of it being disgusting , love is never disgusting your rotten and narrow minded orthodoxies are, them doing so doesn't force you to. For those who say it is unnatural , even fucking oral and anal sex you have every week is , like tell how many things humans do are actually natural , you being able to comment here is unnatural itself, other than eating shitting and fucking( for reproduction) and certain related activites everything humans do is unnatural, like we are the only species to do so from billions that exist on earth. Incest is very much the same , they are ones doing so from among the billions of humans on earth