if we look at other "X didn't really happen" conspiracy theories, the above leads us to expect to find them blaming some particular party for convincing the public of X, in order to accomplish some conspiratorial goal.

Some sort of intentional deception is pretty much the only way you can explain the existence of lots of strong evidence that X happened if you wish to argue that it didn't, so I think the blame angle on those may just be out of necessity to make the whole theory hang together.

It also doesn't really fit the 'see a negative outcome, find someone to blame' because they didn't see a negative outcome, they invented one.

I'm not criticising your hypothesis, I think it works quite well to explain a lot of cases, but I think there must be something else that you're missing.