If discernment and uninformed personal conscience can be applied, as Chapter 8 implies, to divorced and remarried persons, can it also be applied to fornicators? To those civilly married to a person of the same sex? Can it be applied to abortion? How about Euthanasia?
And moving beyond these, can we say, discern a right to pedophilia, to sex trafficking? To usury? To abusing the poor?
If you think that this is a slippery slope argument, that's because it is. But moral relativism often opens us up to slippery slope arguments- and in the long run, slippery slope history.