If it was just a science thing or they didn't care about the security risk, I don't see why they'd keep forming new organizations that are increasingly secretive.
Because it's not just a science thing. It's a potential threat. Threat is defined as capability x intent. We are seeing these things with insane capabilities, but not really any intent (other than maybe observing our technology).
They already responded to FOIA requests, briefed Congress publicly and privately, and announced AARO when they didn't have to. We're pretty well-informed, and Congress has some oversight. It's very ordinary.
The former Deputy Secretary of Defense for Intelligence wrote a blog alleging that there are black projects hidden within DoD contractors that are reverse engineering non-human intelligence craft. He's presented enough evidence to congress for them to add specific legislation to bring these programs to light.
If that's true, then clearly they're doing something about it, so I don't understand why you think they're not doing enough for security. If it is aliens, why would they confirm it and start a race to get alien tech first? You can wait a bit for them to figure it out. If it's not aliens, why would they reveal the details of classified information?