> The bar for mass extinction is much, much lower than the K/T impactor.
Clearly not, otherwise there would have been many more mass extinctions.
In any case, shifting that by a couple of orders of magnitude doesn't save the argument.
Many more mass extinctions, you say? https://en.wikipedia.org/wiki/List_of_extinction_events These are still just the highlights.
Meanwhile, consider what a relatively minor event caused https://en.wikipedia.org/wiki/Year_Without_a_Summer . I don't know the exact size needed for an equivalent meteor impact, but it's a lot smaller than the Chicxulub impactor and we still don't want to get anywhere close to it. Even something like the Chelyabinsk meteor, which injured over a thousand people, would be a half-decent terror weapon.