I know where you are coming from, but in the case of XML, I really think it's bad. I'm tired today so I'm not going to write an essay, but XML's history alone (look up how exactly it derives from SGML) made it a good idea with a bad execution.
Semi-structured data is not bad. Namespaces are not bad. Schema are not bad. In fact, I also on the other hand very much lament that XML's backlash lead us to JSON, which is entirely untyped semi-structured data where everyone has to write an (often buggy and incomplete) ad-hoc typechecker for every single document.
Those features are not the problem, the problem is that they are embedded in the SGML-borne XML, that has many weird and intricate corners that only make sense in light of its history, and that lead to complex parsing, obscure behavior, and lots of potential for vulnerabilities--in the parsers or in code that just uses a (perhaps in itself safe) parser. DTDs, Entities, and Processing Instructions are just some of the more known warts.
Semi-structured data is not bad. Namespaces are not bad. Schema are not bad. In fact, I also on the other hand very much lament that XML's backlash lead us to JSON, which is entirely untyped semi-structured data where everyone has to write an (often buggy and incomplete) ad-hoc typechecker for every single document.
Those features are not the problem, the problem is that they are embedded in the SGML-borne XML, that has many weird and intricate corners that only make sense in light of its history, and that lead to complex parsing, obscure behavior, and lots of potential for vulnerabilities--in the parsers or in code that just uses a (perhaps in itself safe) parser. DTDs, Entities, and Processing Instructions are just some of the more known warts.