It sucks the same way Python sucks. Some people just really don’t like indentation-based syntax. I’m one of them, so I dislike both formats. However, if you groove on that sort of thing, I don’t think YAML is any worse than any other markup.
Oddly, I get along with Haskell, which also used indentation for scoping/delimiting; I can’t explain that, except that, somehow, indentation-based syntax seems to fit better with functional languages. But I have no clear argument about why; it’s just an oddity in my aesthetics.
Humans can be real shits. Still better than finding a starving cat; at least they fed him. Still.
We can put people on lists to restrict their ownership of guns, or driving cars. And yet, there’s no way to restrict people from owning pets, or having children. And folks get right uppity if you even suggest the latter, Left or Right.