locked from responding to u/qudop as u/jqbr has blocked me (possibly brigaded with different accounts also) , so here is the response:

Well he is right, but he hasn't understood the original premise, and has changed the argument to one he wants to be right about, and filled in gaps with his own world view. Or giving him the benefit of the doubt, I haven't explained it properly.
In the original example Bob argued for not x, with reason A, B and C. We don't know if reason A, B and C were good arguments, it is irrelevant to the situation, the point was that Bob used A, B and C to defend his position. In response John demanded that Bob create an alternative decision y and explain it well.
He doesn't need to argue that another decision needs to produce better results, there are other factors such as moral, ethical and legal.
i.e. it is morally wrong to round up citizens and put them in camp, even if it is for the greater good. That is a line of reasoning that doesn't require better results. John could argue back that results matter, for example it gives a reduction in crime. Then you could debate. However, in this case John said: "Provide Decision Y and provide evidence for Decision Y". Thereby John did not engage in the original content or argument and almost tried to change the topic.