Smoking's harms are observable in the short term! You don't need long-term longitudinal studies to show smoking is bad. And we have known mechanisms for that harm that relate to combustion. We know mechanically that vapes are not combusting plant material, and we also don't see the same kinds of obvious harms in the short term. It takes willful blindness to the ills of smoking to suggest that vaping might be as harmful or more harmful than smoking.

It takes "wilful blindness" to suggest vaping can be understood completely today.

We already know there are unexpected side-effects. Like kids starting to go blind, when they start young.

I didn't use Alzheimer's as a random example above. There is a known correlation.

So... Maybe it isn't combusting plant material. But it is probably causing brain damage in some form or another - and that is precisely the kind of symptom that requires a longitudinal study to understand the impact!