Meat and grain subsidies are unecessary. They allow people to eat way more meat than the economy would otherwise allow (grain subsidies go towards feeding animals about 50% of the time). If people got to choose whether their money were spent on meat, rather than being forced to pay via the subsidies, they would not lose out on eating meat if they chose to. However, it wouldn't cost them anything to eat less meat. They wouldn't lose, by not buying, what those subsidies paid for.
As more and more people aware, meat eating causes harm not only to animals, but to the environment, the economy and our own health. Meat is a major contributor to global warming.
By giving people choice, less meat will be eaten in general with no loss to those who want to keep eating as much as before.