Thing is that computers serve an actual purpose (as does talking to people on them). Smoking, for the most part, doesn't. The most prominent thing that smoking does is mess up your health and feed an addiction. Society would not suffer at all for a loss of it.
Video games don't serve any utilitarian purpose, and can be very addictive in their own way. If the secondhand smoking is taken out of the picture (and I mean real secondhand smoking, not "oh no I might have to smell something I don't like as I walk down the sidewalk") they're really in a similar category, albeit to a far lesser degree.
What is a "utilitarian purpose"? People's lives need art and entertainment. Those are useful. Smoking is not useful.
And yes, even if you don't get cancer, smoking can still mess you up big time. No cancer? Great, enjoy your COPD and death by literally drowning in your own lung-fluids.
There are half a bajillion different opinions and facts and non-facts concerning the health risks imposed by smoking. I'm more interested in how you justify videogames being more useful than smoking, personally. Perhaps they are to you, and myself as well, but people have differing opinions of value, utility, usefulness, all that jazz.
The fact that smoking IS a severe health risk is established. It's not a subjective matter.
I can see the use of smoking as a social thing, e.g. someone smoking a cigar on special occasions and special occasions only. But regular, habitual smoking is harmful and serves more of a hindrance than any benefit to the people who do it. It's largely valued due to
addiction.
Videogames are useful for the reasons I stated: Arts and entertainment are productive things for society and have been around for as long as society itself. People need it in their lives. It's a bit higher on the hierarchy of needs than food and water and human interaction, sure, but it's still a necessity. Videogames in particular aren't a necessity, but any form of art/entertainment is going to be require effort and energy and therefore require some sort of sacrifice, and variety of art/entertainment media is a good thing, as they reach/entertain people in different ways.
So... how is smoking useful? You asked me why videogames are useful, and I told you.
As far as people making choices to harm themselves and others is concerned, one function of government is to
prevent this where necessary. People making decisions that harm others is generally frowned upon.
Even if nicotine has a mild calming effect, so do other things; things which don't fuck you up in the long run with addiction and health hazards, that don't make you a burden on society when those effects kick in, don't force you to go out of your way to engage in it somewhere where it won't affect others, and don't cause gigantic industries built around hideous physiological addiction to sprout up and rake in billions of dollars.
As a society, we have to decide when something's negative impact on society and individuals far outweighs whatever small positive impact it has - especially when it causes addictions which damn nearforce people to partake in it even when they don't want to - and decide to either outlaw or at least seriously discourage that behavior, and to curtail the negative effects however possible. This is not a process limited to tobacco; it's just how society operates.