Tiny negligible impact on the industry (Except cut advertising revenue in half, but who cares. What do ads pay for anyways?)
Making the world a worse place? If you look carefully you’ll realize most of the harms and negative effects of technology are due to it being primarily funded by advertising and trying to maximize ad revenue.
I don’t think mobile gaming companies have a potential to destroy free press, or negatively affect mental health of wide population of teenagers, or invade privacy of billions of people. They simply don’t have the scale for any of that.
'I watched an ad, and then [my entire life was destroyed]' is quite hard to imagine, unless it's an ad for an MLM, crypto, entrepreneurship scam, or gambling.
On the other hand, I absolutely know people who started out in soft gambling who then proceeded to throw their life (and sometimes families) away trying to catch the next high with higher and higher stakes gambling until they lost everything, and then some.
We also don't really know the impact gambling is going to have in the near future. Loot boxes, online gambling, internet celebrity gambling, etc. really only became popular around ~2010 or later, and the kids who have been growing up with low-risk gambling as a daily accessible thing on their iPads have not come into adulthood yet.
It is still unethical to even play "free"-to-play games. You are entertained at the expense of a small group of addicts that are often spending more money than what they can afford, and, at least in many games, just being logged in helps create a nicer environment that lures in those people. If you are not there to be a whale you are there to be lure for them. It might not be harmful to you to play, but you are being harmful to the addicts.
The biggest benefit from ad supported tech are search and video, the rest would be better without ads. Reddit would be a better place if they didn't try to get ad revenue etc, in those cases them chasing revenue makes user experience worse instead of better.