Sure it's an ethical call but I'm not sure it's my own personal one. The majority of people who eat meat have no ethical basis; the cruelty involved is, usually, in conflict with their own values (not just mine) - permitted only because 'out of sight is out of mind'. However I don't abandon sustainability just because you have a system in mind that you say is more sustainable.
You do come from an interesting direction; but - reminiscent of your political arguments I think - in putting alternative systems on the table, I don't think you are engaging with the current realities that are the framework for the discussions. I haven't posited my argument within those frameworks. In general if everyone tried to be vegetarian from Jan 1st - vegan even - many would not succeed in this; there would be no danger of a shortage of fertilizer anytime soon. There would be plenty of time to adapt to face whatever reality emerged, so there is no need to argue from some stark, remote endgame. It would be vastly better than what we have at present, and 'your' ideas would still have their relevance. Cheers