The idea is that we shouldn't support veganism because it will mean that eventually, most people will become vegan, and therefore try to ban it completely.
Is veganism invalidated by its unpopularity? If so, then this must invalidate carnism as it's losing market share by this argument. Also, I thought veganism was supposed to be on track to die off because of its unsustainability. It's baffling
"I'm eating meat because if I don't eat meat, then that means the vegans will win! I'm keeping the fabric of our society intact. It has nothing to do with my sensory pleasure. It's actually that I'm really being selfless at this moment. I'm willing to put aside my wants and needs right now and eat this steak as a sacrifice to the greater good because we need people like me to help hold society together here."
If you make this argument, the serious question I have for you is: do you do anything else that others might regard as unethical just because it might be banned? Do you walk around giving strangers yelling curse words and giving the middle finger randomly because it might one day be illegal to do so? This isn't even a coherent position.