My uncle has been smoking for 50 years, suffering no consequences whatsoever.

It must be because cigarettes are good for the health.

/sarcasm

That's exactly why speaking the truth is fundamental, being kind is simply a plus: we all do reckless stuff in life, we all base some choice on assumptions or beliefs, it's usually not that bad, but it can be and someone needs to say it.

Just the fact that we are discussing about an unhealthy diet, that killed millions of people in poor countries, because in rich countries we have doctors and pharmacies and a lot of ways to overcome its dangers and we can't agree that a fact is a fact and choices are choices, proves that being kind before being right can be dangerous.

Doctors will never say "you should eat vegan because it's better for your health", they will say "you should remove this or that from your diet" if something is wrong (yes, bacon is unhealthy too, coke in unhealthy as well etc. etc.) and if you decide to go vegan they will say "it won't probably affect your health, but be careful. Also I want to visit you again in a couple of months".

That's just what it is, unhealthy means not healthy, it doesn't mean deadly at contact!

But people are more sensitive about their choices than their health conditions. People think that their choices defines them, they resist to changes and to facts that challenge their status, because it shutters their reality and trigger their insecurities.

It's not personal, If I say "veganism is unhealthy" it' because it's historically correct and still a cause of malnutritions around the World, not because I think vegans are stupid.

I think they are adults making unhealthy choices (I hope knowing it), just like driving too fast, drinking too much, living a sedentary life or, like my uncle, smoking for 50 years.

My dad worked in lung oncology and doctors couldn't stop some people from smoking even after they had to surgically remove one of the lungs because tumor destroyed it.

Lucky them in Italy healthcare is paid by everybody's taxes or we would have more than a few Walter White.

A popular similar episode happened in the UK, a former very popular soccer player, George Best, had a liver transplant because he drank too much. Even after that he kept drinking and it led to complications and a liver infection that killed him at the age of 59.
Few days before he died he asked to be photographed in the hospital and the photo published with the message "Don't die like me".

It took him 59 years, a liver transplant and an horrible death at relatively young age to understand he was wrong.

Do you think nobody was kind, empathetic or nice with him before about his alcoholism problem?

But how many more were nice with him just to take advantage of his glory, fame, and, of course, money?

Being nice alone serves no purpose, being empathetic or nice, sometimes requires "not nice" manners.

If somebody confronted him and actually forced him to quit, he could well be alive and that liver could have saved someone who deserved it more than a repentless alcoholic.

We should also ask to ourselves: why is it so important for some people to convince others?

What purpose does it serve to have tools (empathy, kindness) to win people trust (they value the messenger), when we have tools (logic, fact checking) to evaluate the actual message?

Back to cigarettes.

Hironically my dad was also an heavy smoker, and reduced it a lot when my mother was pregnant of my sister (she had medical problems while being pregnant of me) and completely quit when my sister was born, because she suffered from asthma.

He went from 3 packs a day to zero in a few months and has been cigarettes free for 43 years now.

He knew he was wrong, he just had no reason to change, he probably thought that without cigarettes he would have lost self-confidence. My mother has always been more kind than right, but she couldn't convince him to quit, no matter how she tried.

Your partner shouldn't convince you to quit smoking or drinking when you have little kids, you either understand it on your own or they make you. There's no amount of discussing the matter that can be considered acceptable. There should be no space for being nice or empathic or reasonable or compromising.

But my dad also taught me that "you smoke years of your life away" (just like Bezos with his grandma, it's true, you really do...) and I have never touched a cigarette before I was in my late 20s, not because I ws scared, but because I thought it was stupid!

I eventually started smoking to make breaks at work, admittedly one of the worst decision of my life, but I like it and keep smoking from time to time, no matter how nicely people advice me to stop.

p.s. many in the comments are assuming that people talking straight haven't tried being kind or understanding before.