The ethical and moral dilemmas concerning food, and food availability, extends to veganism also, just in different capacities.
Often, the moral vegan fails to consider the serious consequences that heavy agriculture has in general. I know that slippery slope is a kind of fallacy, but so is the "meat is torture!!" rhetoric (eg, it also is a slippery slope, the argument then boils down to where on the slope you wish to focus attention.)
To avoid the slippery slope, I view that the human fossil record shows that rapid braincase evolution occurred after humans integrated meat (in the form of fish and shellfish) into their diet. This does not mean that humans NEED meat in their diet, but does hint strongly that the increased nutritional density was/is helpful.
I take to the "non-absolute morality" world view. As such, strongly cased "MEAT IS BAD!!" arguments are immediately red-flagged to me. Since I ascribe more to "moral relativism", I see the focus more in the terms of a spectrum: Which is worse, the extreme ecosphere impacts of intensive agriculture (including the aggressive manufacture and use of nitrogen fertilizers), or the suffering of free ranged beef, with the greater perspective that wholesale removal of industrialized food production (including meat production) would result in widespread human suffering.
Since none of the choices include "no suffering", some degree of suffering must be accepted. When, where, and what kind of suffering is then the context in which to make the rational decision.
Again, the ethical vegan often fails to properly conceptualize the impacts of monoculture, and instead presumes that all animal feed comes from human-edible foodstuffs, which is simply untrue. (See also, humans cannot eat silage. Silage is the left-over vegetable matter of corn production, such as whole corn stalks, cobs, etc.. It is a byproduct of corn cultivation for human consumption, that is used to feed cattle. The notion that it could be diverted to human use is nonsense. Arguments that revolve around this false presumption are rightly dismissed.)