I think it's more enlightening to view it from the other side.

If desktop and mobile advertising didn't have a material impact, why would profit-maximizing companies do it?

If profit-maximizing companies are interested in this type of advertising, what is it about Facebook and Google that captures almost all their spend?

> I'm curious how much manipulation people think is involved in terms of buying things you didn't want. Enough to absolve someone of their financial responsibility for buying?

Well, marketing has some famous stories where seemingly counterintuitive things resulted in more buys, eg. Actimel (not sure whether it is called the same in the US as well, but this fruity milk drink with some added vitamins) was having trouble selling at their original price, but increasing the price and thus making it appear a more luxury item did the think for them. There are many small “hacks” in the human brain that are actively exploited by marketing so while I would not say that we are not responsible for our financing, we are at the very least heavily manipulated when shopping - and also, some people are easier to manipulate than others.