So it’s illegal for Shadowhunters to marry mundanes. First off, this proves that it isn’t just these
asshats characters that are currently in the story who are bigots. In reality, all the Shadowhunters are nothing but xenophobic douchebags who are little better than our villain.
However, I want to now talk about the logical side of this. I’m guessing from Isabelle and Alec’s lineage, that Shadowhunter powers are not only made by the cup, but genetically inherited. Common sense, and the law of probability says that they only a have a set number of people to breed new Shadowhunters from. After a while you are going to have to diversify that gene pool or risk inbreeding. Now, common sense says that Shadowhunters should breed with Mundanes since we are the closest to them on the genetic level to Shadowhunters. Another option would be Downworlders, but I am guessing that a pairing between a Downworlder and Shadowhunters are very rare. Yet, there is a law saying that Mundanes and Shadowhunters can’t get married? What is the purpose of this law, because at this point it doesn’t make any sense.
Another question I have is that since the Mortal Cup has been “destroyed” has the influx of new Shadowhunters slowed down at all? Logically, there should be some type of birth crisis going on, but I’m not holding out hope that this will be at all discussed in the books. They are literally going to breed themselves out of existence because of their xenophobia, which not be hilariously ironic, but will also leave the mundanes unprotected from the demons.