I'm not sure who this author is, but it seems to me he's overlooking the enormous benefit that when a strict xml parser barfs on a file, it's immediately and unequivocally clear which party in a multi party business process is causing a problem and should fix things at their end.

If it weren't for xml, endless (and therefore costly) discussions would ensue instead.

Also, on the more technical side, a barfing xml parser saves you from having to spend hours hunting for subtle bugs introduced by a permissive parser that is permissive in ways no one really understands fully.