It's a tricky one, certainly.

There is probably a graph somewhere showing how much effort to fix is too much effort, vs how much bad will in the community this project is inducing, vs how much value this project has.

So no, Apple's system being jammable is a great "booby prize" right up to the point where Apple fix the algorithms, or the chinese government start reporting these false positives as bugs and saying that Apple must fix the bugs before their devices can be sold in China.

And so, one has to assume that if the algorithms can be fixed, they will be fixed. If we can DDoS Apple's human checking capability while it's still young, we might be able to prevent more resource being sunk into it - though I agree, that's unlikely. If we can do all that AND make it clear that this is going to cause nothing but bad will, and if we can get enough governments to regulate against it, then there may be hope.

So your question was, why do people think this software isn't going to work, and the answer is we really hope it isn't going to work and really hope that enough people get onboard with the efforts to subvert it and really hope that the message sinks in to Apple that this was a doomed project that they should abandon for good.

But with enough money and time, there is no problem that can't be overcome. So even if it is a currently jammable child protection system, in the future is will almost definitely become a robust human rights violation system. In the space between those two points there is hope. Slim hope, but hope nonetheless.