XML isn't bad in and of itself. It's just a powerful, neutral format. The problem with XML is that it allows so much abuse.

I had to interface with a government system at some point. They shipped us a whole schema of custom elements such as "IsShipment" (for example) which extended bool to allow extra options. All this was clearly documented in the schema comments "You can use 'true', 'false', 'sortof', and 'mostly'." So we go to validate the data.... and it doesn't validate. Against their schema. Because they didn't extend bool, they just said they did in the comments. When we got back in touch with them, we realized that they had no clue that the stuff not in comments mattered. As far as they knew, XML was just text, and they had clearly specified how it was to be interpreted (in English).