What? Of course it is! There are physicists looking for the unified theory who hypothesize that there may be a unified way of understanding all the forces. IANA physicist by any stretch so maybe I've misunderstood the Great Courses and books I've read, but gravity is actually quite poorly understood to us currently.

But the broader point about things not being open for debate is dangerous, and I think you unintentionally demonstrated a real-life reason why. If we stop questioning gravity and trying to understand it's cause better (which IMHO primiarly happens through reasoned, intelligent debate) then we stagnate, and stagnation can be dangerous as from there it's a short hop and a skip to regression.

If you want to make the argument though that some things aren't open for debate, I think there are stronger cases, like the Cartesian "I think therefore I am" is hard (though not impossible) to argue against because it forces the thinker to make arguments for their own non-existence, which is a tall order for a person who by definition must exist in order to do so.