I'm vegan too. My reason for being vegan is entirely on the basis of sustainability. If lab meat is produced in a sustainable fashion then I'll be all for eating it.

I really doubt lab grown meat will ever be as sustainable, as a normal plant based diet.

I wouldn't be so sure, it takes a lot of water to grow food.

Economies of scale. I think the product will become financially viable faster if it has wide-spread vegan support.

One would only be on-board with that assuming they were on board with the whole of the product. So first you'd need to make the argument as to why a vegan should be behind this product, besides "more people can afford it if all vegans buy it."

Also, that only works if it has competition, otherwise, if it were that popular and there were no competition the producer would have good reason to raise the price knowing the market could bear it.

One nitpick (was going to be two, but I mentally nitpicked my own nitpick) economic theory suggests that if the artificial meat industry had a decreasing long run marginal cost with increasing quantity then the price could actually decrease as a result of greater demand.