People I've met who might've been involved in IC don't talk about it, at least not with me (and I assume it's improper to ask), but I did once meet someone peripheral to that, who vocalized one kind of thinking about it.
Years prior to the meeting, around the time of the Snowden thing, in a private research forum, I said something like: one of the IC orgs did important work, etc., but seemed to need guidance on Constitutional balance. It was a random comment, and I forgot about it.
Years later, I was meeting with someone from that forum, about a (non-IC) job, and their attention was divided with laptop while they talked with me, like they were also reviewing my resume or something. Suddenly, they were agitated, and seemed to be referencing -- not our conversation, nor my resume -- but my forum comment from years earlier, as they angrily started saying how people at such-and-such org "know the Constitution better than anyone", etc. Then angry impromptu speech about (public) information about threats, and (public) information about a claim of why such-and-such org had done certain things.
I'm somewhat sympathetic to that, and I also realized that I needed to get the interview-gone-sideways back on track, so the discussion recovered after that. But at the end of the interview, there was obvious (renewed) irritation in their voice and manner. (And that's not my worst interview ever. :)
I realized that the person's work had probably led them interact with IC orgs before, the person had been impressed by the orgs, was very concerned about threats, and was offended on behalf of the org by armchair critics like me.
I imagine that person is not the only one with strong feelings like that, but that people actually at the org, and who had similar feelings, wouldn't speak with an outsider about it.