It would take a bit of math to ascertain but I would be reasonably certain that smoking has a higher fatality rate than Covid-19. The businesses that sell cigarettes have had no issue staying in business for centuries - and they even continue on today, profitably.
I’m sure that there’s some fatality rate that would make people get a bit more realistic about their choices in life, but it’s not in that territory. Twitter will be okay.
Likewise, cannabis smoking is probably bad for your health. The smoke is unfiltered and so more carcinogens are getting into your lungs and, it’s probably going to increase rates of lung cancer among frequent smokers. It is also looking likely that it will end up showing negative effects on brain health, as well. Should Twitter be telling people that they can only make posts that amplify the negative effects of cannabis?