There is some evidence that Tor has posed significant problems for three-letter-agencies in the past, so it's not like there is nothing to be done at all.

But there is a bigger point to be made: in my experience most privacy activists argue that taking an absolutist stance personally is counter-productive -- just because it is almost impossible to completely eliminate risks from your life does not mean you should give up and not try to minimise them. And of course, the goal for most people isn't to protect against targeted attacks (since that means you already need to take fugitive-on-the-run-level precautions), it's to avoid becoming a target in the first place.