If it was produced initially from an animal, there's still harm done, although I'd argue it's infinitely small compared to what it achieves. There's also the fact that many vegan people try not to purchase vegan products if they come from a "non-vegan company". So if a meat producer also starts peddling tofu, vegans will buy from a different brand simply so they don't line the pockets of the meat or dairy industry. With the way things are going, I'd imagine the first to achieve lab-grown top-quality meat would be an agricultural/farm corporation, which wouldn't sit well with many vegans.