Not disagreeing that policies should be made with success in mind. But by the same reasoning "vegan" should include the top 5 most popular meat dishes as exceptions. This would easily make it more popular, more accessible and probably much more successful at reducing meat usage over all. The issue is that the definition of "success" might be entirely unacceptable. Just like "entirely free but...." might be unacceptable.
In all fairness, flexitarianism is a thing, and I know a lot of people who would never want to go fully vegetarian or vegan, but who want to reduce their meat intake significantly, generally for environmental reasons. The change in messaging from "a single animal death is murder and unacceptable" to "any reduction is good, the more the better" is probably significantly not effective in this context at actually reducing overall meat consumption (although I unfortunately don't have any evidence for that hunch).
The first time I tried becoming vegetarian I failed. I often had no reasonable options in restaurants nor social events. Also I live in a country where meat is cheap and barbecues are a key social activity.
Nowadays I still eat meat 0-2 times per week when my choices are limited, but that's much better than eating 14 times per week.
If you consider the fact that veganism/vegetarianism is very unhealthy without taking the nutrients you're missing as supplements (which could be argued as being "reverse engineered meat"), then I would suggest that yes, until we reverse engineer the "meat" we should include it in the "diet" (along Free software).
Not disagreeing that policies should be made with success in mind. But by the same reasoning "vegan" should include the top 5 most popular meat dishes as exceptions. This would easily make it more popular, more accessible and probably much more successful at reducing meat usage over all. The issue is that the definition of "success" might be entirely unacceptable. Just like "entirely free but...." might be unacceptable.