There is no reason because it's not true. I've used the with statement to help with auto-closing tags (and just readability) in templating and it helps a lot. I've used in on sites which received over 1 million hits a month. It's been used on over a dozen sites and projects from hundreds of lines of codes and even into the tens of thousands of lines of code.
> Please don't abuse with for XML/HTML generation
Being guilty of such abuse, I would like to know why not? (I genuinely want to know!)