I'm not proud of it at all. The revelation was startling to me, and I was pretty unhappy about it. It was done in the name of "stopping bad people from doing bad things", but it was still illegal (at least in the white world).
Snowden had the same dilemma. He was asking the NSA lawyers about the legality of their programs, and he never got an honest answer.
Quitting would not have stopped the activity, and disclosing it would have subjected me to the same treatment that Snowden got.
(Years later, I heard an NSA program manager boasting that they would keep asking different government lawyers for an opinion on the legality of proposed programs until they got the answer they wanted. This was after Snowden's revelations.)
Pretty much everyone in CIA has a "ends justify the means" philosophy. It's easy to fall into that trap when you learn about all the devious things our enemies are doing.
Apparently EOs have been used to circumvent the constitution for quite a while.
Quitting would just be the first step in "I do not want to participate in this". Whistle blowing is much more complicated in that you are hoping to not just not be participating but maybe stopping it altogether. Being young and single compared to being older with dependents would absolutely make that decision harder. Violating secrecy laws to disclose illegal activity seems like something that should have a caveat to allow, but of course they don't.
Every administration effectively creates their own interpretation of what is permissible in this regard. The rules of engagement as it were that are set down by each administration vary widely. Nonetheless, it has effectively become a one-way ratchet.
The "ends justify the means" mentality in various government security agencies is very, very real.
It's easy for others to say, "oy, you coward, you should have blown the whistle" from the comfort their web browsers. For what it's worth, I had a security clearance in a previous job (not as high as yours, I'm sure) and I understand where you are coming from. I would have likely done the same as you. Especially with my career and the ability to provide for my family on the line.