I've given up debating this with the COVID skeptic folks because it's impossible to definitively prove exactly what would have happened without lockdowns. Instead my general argument is that it was a situation where a great deal was unknown, if with the benefit of hindsight we learn that we overreacted that doesn't mean the original choice was the wrong one. We worked with the evidence we had available at the time and we played it safe. Playing it safe seems sensible to me.