Sam;1311 - No. And this is obvious but I will say it anyway - message history is only viewable by yourself and the contact you were chatting to (or the group in the case of 'group chat'). Don't want anyone panicking.
I strongly disagree! If these are my messages, than I should be able to read, write or delete. You, as server admins, are the third that can also access all histories stored. All messengers have an user and a password to protect personal information, but they don't rely on that. You shouldn't either. Again, I don't like not being able to delete my own history. It makes me feel like it's an official investigation, not a messenger!
Not to mention it is a waste of resource for the mainframe.
The idea is that there should be an opt.in option, not an opt.out. Instead, you are talking about not being able to opt-out. And we are taking about all time history!
Regards