Are most internet ads scam?

This is an example why I will never try to make money off my website and blog by running ads. I saw this on Freethought Blogs website.

Yes, the notion of "healing the water" meshes so well with a scientific approach to the world. And yet the ad selection software (probably run by a third party) keeps putting ads on Freethought Blogs that directly undermine their message. (Even if Freethought Blogs aren't specifically oriented against pseudoscience, it is a big area of scrutiny in the freethought community.) At the very least the ad rotation software needs to be more semantic-aware, to gauge the attitude of the target audience towards the ad. There was a time when New York Times could also benefit from a similar intelligent filter, at least in their Science section; ads for a "quantum healing" change-reality-with-your-thoughts self-help course might not sit well with the audience who wants to read about physics. (I haven't seen those ads on nytimes.com in a while; maybe they got wise to it.)

But if better semantic analysis eliminated every ad promising $$$$/week working from home, or one "weird" tip for a flat belly, would there be any ads left to run?

I'm exaggerating, because I do see ads for useful products, like shoes, handbags and cell phones, or Dell servers and programmer outsourcing firms (I guess data mining algorithms must have concluded I'm a female CTO of some company. I should feel flattered. :-)), but those are no more than 1/3 of all the internet ads I see. It is just me, or is it really true that overwhelming majority of internet ads are snake oil products and scams?

If so, what does it say about the whole business model of advertising-supported websites? Companies that have something valuable to sell don't seem too interested in advertising on the web. And yet many startups count on being able to survive off ad revenue. I wonder if they are being naive about this whole concept (and given the rate at which they go under, they may be) -- unless they count on there always being plenty of idiots to fall for scams. (That may be not a bad assumption, sadly.)

I've seen some too-good-to-be-true ads, e.g. hot stocks and ridiculously cheap car insurance, even on websites of major U.S. newspapers like Washington Post. Is that an indication of just how desperate for cash newspapers are?