It's all good, since MR currently leaves individual posts editable (at least I just changed one from Feb 2011), so a user can remove or change
any specific information from individual posts if they need to. I guess people ask for bulk deletion, but I think there's normally no need for that due to security or privacy reasons, other than "convenience". If it means that much to someone, they can go through their posts one by one, if they need to. The only sticking point is if they get quoted on the now-sensitive material.
That seems a reasonable compromise to me, on the posts. It would be courteous to support deleting an account (with the requisite e-mail addy) without affecting the posts, but users can work around that as stated above.