Demos from a 3rd person, I agree, not very useful, first-person would have been much more interesting. But even from a 3rd person demos is not useless and can show the fact of the rapid emergence of a player after his death, in the absence of wallhack spot, etc.
But this is offtop, conversation in this topic for talking about screenshots.
Yes, I can say that there are workarounds screenshots and I say this from experience administering BF2 servers, but nonetheless screenshots PB is one of the methods of protection and very good