It depends on whether you consider vaccines and human intervention as part of the 'natural' feedback process that tends to make viruses less severe.

In other words, the high-level theory is that more severe viruses either kill their hosts, or make them so sick that they stop interacting with other potential hosts. A form of social distancing, if you will.

In both cases, the virus is triggering some form of behavior change in its host that reduces its reproduction, providing evolutionary pressure towards milder viruses.

One could argue that the development and wide distribution of a vaccine is just one form of host behavior change, and should be factored in.

And the reason we pursued vaccination rigorously enough to eradicate it was because as you say it is very deadly and very contagious.

Something with a mortality rate of 30+% and kills children at orders of magnitude higher rate than COVID has is far easier to convince the world populace to vaccinate for than something with 1-2 order of magnitude lower CFR.

So you can most 100%, certainly say, it was eradicated because it is so deadly. If only say 0.5% of people died from it, disproportionately the elderly those with comorbidities, eradicating smallpox would have been a hell of a lot harder to get worldwide vaccinations on board. A hell of a lot.

I don't think they're disagreeing with you, just saying that one cannot "ask smallpox" because it's already eradicated.

Smallpox still exists as lab samples. It's in virus prison. It's not dead.