I think danShumway answered 1) pretty well. I just wanted to add my opinion about 2).
Nothing an individual does in terms of personal behavior can have any "significant impact" at a global scale. If all humans made decisions like this, we would all come to the same conclusion, none of our individual actions are responsible. Which, while true, is ultimately a useless conclusion. I'd rather that we as a collective change our fundamental behavior for the better instead of governments imposing on our lives. If all governments decided tomorrow to ban all meat products, the world would undoubtedly be in a much better place. You also mention second order effects (small circle of influence) but even that is marginal. Being a vegan, I believe I've "converted" (just by exposing them to an alternative lifestyle) two people to vegetarian.
This is another classic example of Tragedy of the Commons [1].
Outright bans will likely never be feasible at all, though we could (and should) consider banning many of the bad practices that usually come with large-scale factory farming (and publicly funding grants/subsidies for these plant-based alternatives).
I prefer the equivalent but opposite legislation, remove meat and dairy subsidies. I don’t have faith in governments to constantly fine tune subsidies to the right things. Subsidies just become a means for politicians to pass money to their constituents. It took Canada 60 years to stop emphasizing cow milk consumption in their dietary guide, I have very little faith in governments to get things right let alone in a quick iterative fashion.
Nothing an individual does in terms of personal behavior can have any "significant impact" at a global scale. If all humans made decisions like this, we would all come to the same conclusion, none of our individual actions are responsible. Which, while true, is ultimately a useless conclusion. I'd rather that we as a collective change our fundamental behavior for the better instead of governments imposing on our lives. If all governments decided tomorrow to ban all meat products, the world would undoubtedly be in a much better place. You also mention second order effects (small circle of influence) but even that is marginal. Being a vegan, I believe I've "converted" (just by exposing them to an alternative lifestyle) two people to vegetarian.