Unless I'm mistaken, there is no Hollywood-approved way of getting a movie in such a format that allows to apply your own subtitles to it. Therefore, all the customers of this site are pirates, and annoying pirates is what the Copyright Industry does.
From their point of view, it doesn't hurt their customers in the slightest, because their customers don't need subtitles (and if they did, they wouldn't be able to use them either way).
Bypassing DRM is only illegal in some countries so if DeCSS is legal or not depends on where you are. But you are right even legal bypassing of DRM is not Hollywood approved.
From their point of view, it doesn't hurt their customers in the slightest, because their customers don't need subtitles (and if they did, they wouldn't be able to use them either way).