Earlier quoted context omitted.
Cheap soybeans makes meat cheaper, but the production of meat is inherently inefficient. If the production of meat substitutes from soy could be made more efficient than the production of meat from soy, then de facto soy subsidies would disincentivize the consumption of meat.
I wouldn't say subsidies would disincentivize meat. I would say they would incentivize both meat substitutes and meat, in an equally proportional amount.
Say it takes 50 cents' worth of soy and 50 cents' worth of other expenses to produce $1 worth of beef, and it takes 90 cents' worth of soy and 10 cents' worth of other expenses to produce $1 worth of meat substitute. If the effective price of soy falls by 10% due to subsidies (and other costs remain the same), the cost of beef will fall by 5%, while the cost of meat substitute will fall by 9%.