There are many reason why Hosie shouldn't happen and why it just a plain old terrible ship.
1. It doesn't make any sense.
2. They have little to nothing in common. - Think about it, the only thing they have in common is that they're witches and they're not as bad as Lizzie.
3. They're sorta like family - The three girls(Hope, Josie and Lizzie) knew and kinda grow up with each other since they were little. Besides that, even though Alaric's not Hope's father, he's her guardian. It not technically incest, but it's in that area.
4. It makes more sense to ship them as friends - It makes more sense for them to be friends.
In conclusion, Hosie has many flaws and it doesn't make any sense. Posie is where it's at. If you look at the facts, Posie is the better ship.