Everybody has the right to publish what they wish. They have to write it. They have to find and sell it to a publisher. The publisher has to take the risk as to possible sales. After all of that the public is free to buy or not buy. Please note there is NO requirement or a truth commission to prejudge a books contents prior to publishing.
It is obviously easier to sell a second book if the first does well. Something about a track record of successful sales.
When menzies first book was published I visited this board indicating the books theory (China was here first) really had no new solid basis for the claims. The claim itself was orinally based upon Menzies belief that portolano charts etc suggested a worldwide sailing knowledge set prior to the arrival of Columbus and western explorations. What menzies did was put a Chinese face to that. It on the face of it seemed pausible because ot the Chinese admiral and his fleet of ships. Pausible or not menzies offered no new evidence that it actually occured.
This kind of supposed knowledge set also undelies much of GH's works. As he has said there seems to be a collective amnesia as far as humanity is concerned. Others will continue to try to put a face of some sort to that possibility. Even you.
Debunking books hardly ever have a successful track record. Thats in the nature of the thing.