It is the same with anything people are passionate about. Each side thinks they know better. The pro vapers seem defensive to you because for them vaping has made a huge positive difference in their life and the arguments against so far are based on speculation. I react the same way when i see those silly paranoid mothers refusing jabs due to whatever flavour of conspiracy they prefer.
So you're equating vapers refusing to acknowledge negative health impacts of vaping to mothers refusing to acknowledge the danger of refusing jabs?
It isn't the same as anything people are passionate about, or at least that shouldn't be an excuse for being blindly defensive of anything. People being unable to acknowledge that there's middle ground in almost everything and take an educated and objective view is quite frankly ridiculous given the amount of information available to us nowadays.
Vaping is probably not as bad as smoking, but it's probably worse than doing nothing. How much worse is a relative unknown at the moment, and it should be treated with caution in the meantime - especially in cases where passive inhalation is occurring. There's really no more to be said about it than this.