I regard people as intelligent beings capable of independent decisions and conclusions. Therefore, I do not see anything unethical in such advertising. If it is very easy to deceive you (or rather create a mistaken opinion) with the help of such simple techniques, then this is first of all your problem and you need to raise your level of awareness and a critical view of the world.
That really depends on life circumstances. Is someone taking drugs and getting addicted to online gambling automatically less intelligent that someone who doesn't get into that situation? I would highly doubt that. You can be in personal trouble or whatever problem you might have in a certain situation, stuff that can make you vulnerable to bad influence that usually wouldn't harm you in the slightest.
Also, age plays a big role. I have made bad decisions with 15/16 years that I would never repeat again.
But if you exclude age, then everything that you have listed - drugs, some personal problems, illness, etc. it is not a problem of who is doing advertising or is your counterparty in any transaction. If a person is considered capable, then all his decisions are his responsibility. Because if you consider it differently, then unexpectedly for yourself, you may face the cancellation of transactions unilaterally and other things due to the fact that the counterparty "had some problems".
I would argue that you are a bit wrong here to say the least. We have some very dangerous tendencies in society not because people are less intelligent today, but because it is easier to be influenced by things that sent you off your own path, the path you would take by making your own decisions without being overwhelmed from the outside.
Diabetes isn't rising because people are less intelligent. Same for porn addiction, it is just the availability. People socialize less today because of social networks and the digital space growing, and many of those things happening these days aren't healthy.
And where is the line when you would say someone is capable or not? Also, it is scientifically proven that there are people who are genetically more receptive for addictions than others, so are they less intelligent?
I am not speaking against advertising stuff, but luring people into buying something with dubious techniques is questionable. One was mentioned before and that is when someone gets paid to play online casino games where something might be rigged. You see, it could even be rigged without the streamer knowing about it I can imagine. Like they get paid $10,000 to play on a website, and what a lucky they have out of a sudden, they keep winning and winning because there is a wonderful software running in the background and they don't even know about it.
I think as soon as advertisements strongly tend to portray false chances or promises, that is a red line.