https://www.cdc.gov/tobacco/e-cigarettes/health-effects.html
Why would your default assumption be that putting foreign (and poorly regulated) substances into your lungs is more likely than not safe?
This is especially true since it’s a drug that doesn’t even have much claim to fame for positive recreational or medicinal benefits.
I'm not claiming that vaping is safe in some absolute sense, it wouldn't be surprising if there are some meaningful health risks. I personally do not vape myself because the times I've tried it, I've found getting the vapor into my lungs to be very uncomfortable. But it does seem like it's a strict health improvement over tobacco smoke, given that the CDC can't articulate a specific harm to the lungs caused by vaping.