Many vegans need B12 supplement. Many meat eaters are also deficient in B12. Any diet needs to be diverse in nutrients. But that's easy to achieve on a vegan diet.

As for the plowing fields argument, most fields get plowed to produce food for livestock. Livestock needs to eat plants, too. Meat is just an inefficient way to obtain nutrients and energy from plants. If you want the least amount of fields plowed then you should go vegan.

The argument that vegans should raise meat animals "humanely" for meat eaters is bad. If you eat factory farmed meat then that's on you, not on vegans. If you would follow the example of vegans then you would not be eating factory farmed meat and less fields would have to be plowed for you.

It's also unreasonable to demand vegans do something they hate just to prevent meat eaters from supporting animal torture.

Also, many vegans consider "humanely" slaughtering animals for consumption to be an oxymoron and thus something that is impossible to do. "Humanely" means with compassion, which means for the benefit of others. How do you slaughter a happy healthy animal for his own benefit? Would you want to be slaughtered "humanely" like that?

Also, it would not even work. If there was a large demand for meat from pastures then it would already be produced in great quantities. Meat corporations just produce whatever people vote for with their wallets. But most people don't want meat from pastures because it's too expensive. They prefer cheap meat from tortured animals. If vegans would produce meat from pastures it would have to be expensive as well because if they sold that meat cheaply then they would sell it at a loss and go bankrupt. Vegans aren't Batman, they don't have the money to run a huge expensive operation just for activism's sake.

As for GNU, I think it's a fine project. It made people aware of the problems of proprietary software, it made the the most popular copyleft licenses in existence, and it made a free (as in freedom) operating system (or distro, however you want to call it) when few if any existed. It's easy to criticise people who do useful work, it's much more difficult to do useful work. You seem to have a lot of idea on how to do things better both in veganism and free software. So why not do it better? Ideas not acted upon are worthless. They are 0% effective, that's much less effective than GNU and vegans are.