Since the author of the post is also an author of LLVM, clang, and Swift, and the director of developer tools at Apple, he certainly understands the difference between sloppy and non-sloppy code, but he also knows that sloppy code is a reality and undefined behavior is dangerous.

So we can make everyone a better programmer, or we can make better languages, or we can throw in the towel and say things are good enough. I think he's suggesting the correct path.