I wrote the Cog briefset on this last year for the Stoa resolution. It was very interesting. There actually is some good academic stuff to defend FISC but it took some digging.
I don't see any defendable Negative stance
A smattering of what I recall from the research:
-While FISC hasn't significantly blocked the NSA, they do 'steer' the NSA to mitigate problems. So they don't say "you can't do that" but they do say "if you're going to do that here's some steps to mitigate privacy loss".
-Claims that FISC is a rubber-stamp approval are based on the extremely high rate that they accept executive proposals. The response is that there's solid detailed dialogue on all steps of the process, so the executive knows what will or won't fly before they even officially go under FISC review, so they've already adjusted to the judicial demands.
-And a fun one. Basically claiming the executive is going to be doing this surveillance anyway, and if FISC was transparent and aggressive then the executive would totally ignore it. If FISC is secret and accepts a more minor role of mitigation they can at least have some positive impact.
While I'm not a fan of much of the NSA's practices, I see that as primarily an executive problem, and then a problem of congress and the Supreme Court to just let it all slide. FISC operates within a whole federal structure that prioritizes security way above privacy, and given that limitation there's at least a defensible case that it's doing the best it could do.