Grocery stores and Fast Food restaurants like McDonalds often reduce the price of commonly bought food products like milk and cheese burgers below levels that are profitable on their own. The reason for this is that average people going to stores make quick comparisons of commonly bought items rather than doing any deep economic analysis: “This store has cheaper milk than store X, I should shop here!” This loss leading strategy attracts people to stores, to buy other things that lead to a net profit. Fast food restaurants charge considerably more for soda than it is worth, but since it is a complementary good, people buy it.
So if you are vegan, and you go to McDonalds, what happens? You pay more, despite your food being cheaper to produce, and you increase their profits more than meat eaters do, enabling them to sell more meat at a loss. If vegans were the majority of the population, meat couldn’t be a loss leader, but since they are a small (but growing) fraction they might just be subsidizing meat eaters. While it is true they reduce demand for meat at the McDonalds level, if the entire vegan population began eating loss leading meat products exclusively when at such places, would McDonald’s really try to buy more meat from factory farms as a response when doing so will lose them money?
It may be the case that burgers aren’t really a loss leader, that they are merely profit neutral, or that buying a loss leader on the margin increases profit since the fixed costs have already been paid. Even so, paying too much for vegan food is still subsidizing the cheapness of meat for everyone else. At some level of vegan strategy (assuming the goal is reduce animal suffering) you just shouldn’t eat at certain places, or you should pay less, hurt them by eating a loss leader, and donate the rest to some effective animal charity (though it may be hard to decide on one).
A weird situation that can happen here though is if vegans are divided on the strategy. If one half eat veggies that are over priced, and the others just eat loss leaders, they average out to be just like normal people (though maybe donations to animal charities make this not so bad).
Personally, I’m fairly vegan, but I do have a rough cost curve in my head, and there are lots of situations I will eat animal products (though the overwhelming majority of these involve free food/ not increasing demand). I’m also fairly apathetic on dairy, I think that while cows suffer from separation from calves the marginal suffering for consuming dairy is tiny and that if you are going to optimize on that level there are a bunch of plants you probably shouldn’t eat for ethical reasons as well. If effective animal charities are as effective as Animal Charity Evaluators has claimed, cost cutting should be overwhelmingly more effective than being 100% vegan: if it saves you a buck to get the same level of nutrition/taste/etc. in a given meal by eating not vegan , you donate the dollar saved and the marginal effect is multiple animals saved from factory farming, then you are helping animals way more than normal vegans. Being vegan on its own is not a particularly effective way to be altruistic.
Fortunately vegan food can be pretty cheap. Things like Soylent are time saving, vegan, and not bad tasting (in my opinion). If you are more price sensitive, off brand versions of Ensure Plus store better (great for disaster situations and reducing number of transactions) are very cheap, faster, lacto-vegetarian and balanced (though they have more sugar, it isn’t above the RDA). Rice and oats, beans and lentils, dark greens like spinach, kale, and broccoli, and cheap fruit like bananas (another loss leader) and apples can all make for really decent staple foods at low cost. If you can’t tolerate veggies and meal replacements, there’s always micro-nutrient pills to subsidize whatever you can eat. If veggies are expensive, you can always get them canned or frozen. If you can’t normally get enough protein as a vegan, and aren’t gluten intolerant, you can get 127 grams of protein per dollar.
Overall, there are a lot of ways being vegan can be cheap, and if your vegan food is low cost, you probably won’t be subsidizing meat.