>Would it be crazy to say sitting on exploits is effectively "inserting a backdoor"

That seems intentionally dishonest, no? If I disagree with a position I'm not justified in intentionally misrepresenting it because I feel morally correct. Unless you're alleging that these vulnerabilities were intentionally placed there, I don't understand why you'd feel the need to say that. Worrying about the effects of stockpiling vulnerabilities seems like a defensible position in and of itself.