I saw an ad a while ago for a piece of software that turned out very beneficial for my business.

I did not know that such software existed.

The ad was good for me and for the seller.

Trade is not a zero sum game.

That's entirely untrue. I'm a photographer (though I'm largely quitting after this year) and advertise on Facebook/Instagram. If someone was in my area and got newly engaged, they might see my ad. They probably need a wedding photographer, and they're only going to actually go with me if they like the look of my photos better than everyone else and my price is within their budget. Without advertising, they might not be exposed to my work and end up with someone that would take worse photos for them.

I also used to 'boost' my high school senior posts to other 16/17/18 year olds in whatever area they're from. Not only did that work as advertising for me, all of the likes that the images got from that probably really boosted the kid's self esteem. Within the past year they made it so that I can no longer target people under the age of 18 by area.

This is just plain false. At best ads will inform you about the existence of valuable products, services and opportunities that can make your life better. Every business must communicate with potential customers. Personalized ads are much more likely to be something you might want than the generic billboard on the side of the road.