You need to know when to stop in everything, especially with hard-to-digest, high-protein foods. Also, take into account all the characteristics of the body. After all, for one the product can be useful, and for another - a real poison.
Meat is a good source of protein, with a high content of essential amino acids (i.e. those that a person cannot produce on his own), which are necessary for the normal existence of the body. Yes, these same amino acids are present to one degree or another in other foods, but it is much easier to get them from meat. The total protein content in a balanced diet should be approximately 10-15% of the total energy value. Meat is also an important source of fat for the body (which, again, should not be ruled out).
Now about cancer and meat. Research shows that there is a strong link between colonorecal cancer in populations and the amount of meat consumed by those populations themselves. However, the main explanation is the direct cooking process at high temperatures, as well as reactions with smoke, salt, and others. The products of such reactions can react in the large intestine and turn already into carcinogens.
Ducan doesn't say "eat a lot of meat". Ducan says "limit your carbohydrate intake." They are far from the same thing. In my experience, the Ducan Diet does allow for quick weight loss, but it is not designed to keep it constant. In this sense, the Montignac diet is more effective and more enjoyable.