The following is my real-world take on this subject, directed at no one in particular, but at everyone in general who is critical or afraid of XP (often the same people who don't have meaningful experience of using it):
XP is a process that has *evolved* through the collective experience of programmers through the mess that the software industry had become- always late, always over-budget, always buggy. And we were told to accept it as a fact of life.
In the midst of all the chaos, there were programmers working after hours doing what they weren't allowed to do during the day - writing tests for code (TDD), automating builds and tests (continuous build & integration)
XP and Agile brought us all out of the closets. That's why only experienced people with open-minds find it easiest to adopt XP. Or fresh out of college students or young programmers who have not yet been corrupted by the "you're too good to write tests- you'll only do coding" crap they often get fed.
To me, questioning XP without learning XP is like questioning the Gang-of-four Design Patterns before you have any serious programming background solving the problems solved by the GOF patterns.
Design patterns *evolved* after years of people doing things the wrong way, before they learned the right way. Design patterns teach us how to write good code by learning from the mistakes made by smart, experienced programmers before us and the lessons they learned.
*** Design Pattens are Best-practices for programming, solving most typical programming problems.
*** XP/Agile are Best-practices for product/project development process, solving most of the typical process problems (requirements gathering, estimating and scheduling work, measuring progress, managing change, getting feedback early & often, continuous knowledge transfer and peer-review, ... the list is long.