Ontological impossibility ≠ intrinsic evil. Abortion, embryonic stem cell research, and euthanasia are intrinsically evil because they violate . The simulation of a sacrament (ie. two same-sex parties being joined in “marriage”, oreos and milk being used for elements of consecration, communion at a Protestant service, etc.) are not evil. They just don’t work because that’s not how God intended for the sacraments to be confected. One should not partake of them, that would be bad, but that is not to say that the group of kids playing mass are somehow being sacrilegious or engaging in an “evil” activity, anymore than the Lutheran minister who performs a communion service. I think you’re conflating same sex sexual activity with same sex marriage. Same sex sexual activity is a grave sin, yes. It does not logically follow that since same sex sexual activity is a grave sin that same sex “marriage” bears the same penalty of sin that the ss sexual activity does. They’re two separate acts/events and don’t mirror or equal each other.
Just thought I’d clear that up.