Veganism generally postulates that fundamental social change can be brought about through ethically conscious change to consumption within the existing economic system. Such an argument ignores the fundamental reality that in capitalist society, it is the owners of the productive means who decide what is produced and the methods by which this production is undertaken.
Driven by the inherent necessity to accumulate and realise profit, individual capitalists utilise cheap methods of production in an effort to market commodities competitively. In this sense, meat is no different to any other commodity. Under capitalism, moral questions of humaneness are completely subsumed by the requirement for capitalists to realise profits.
The environmental damage and cruelty towards animals wrought by capitalist producers is not influenced by matters of consumption. Supermarkets who readily sell meat en masse also generate revenues through the sale of meat alternatives and vegetables. It is nonsensical to argue that the purchase of non meat products are not linked to the production and distribution of meat products themselves. Indeed, the financial links between those who produce meat and non-meat alternatives is an area which requires significant further investigation.
This is not all, consumption under capitalism is inherently problematic for veganism's objectives. In a system where the working majority of society is separated from it's sustenance, cheaper products find their way into the basket of goods which facilitate the continued reproduction of the labour force. It is exactly these low value, low quality meat products which impose cruelty upon animals and poor nutrition upon exploited workers. It's also likely that for every vegan consumer there is another who consumes meat in excess; evidently, this is an issue of production rather than consumption.
While it may appear contradictory to argue that reducing meat consumption has no impact whilst active consumption does, the point acts to illustrate that you cannot wholly eradicate the consumption of a basic foodstuff while operating under a structured and exploitative economic system.
For as long as the exploitation of workers continues, the consumption of the majority of society will continue to be influenced by low cost commodities, introduced to the market to realise profits. Capitalism cannot be reformed in the interests of workers, the environment or indeed in the interests of animal rights. These interests can only be represented in a democratic society freed from the private ownership of the means of production and the artificial constraints of the profit motive and the wages system.