Registrations per se are not unethical or "evil". It's the way the collected data will be used in the future that may (or may not) be unethical or "evil". I think, for example, that registering for a piece of content or information at www.ibm.com after clicking an ad is less risky than registering at www.widgetdeals4cheap.com where no other information (i.e. other than the registration itself) can actually be seen. Why would I care to register to see deals for widgets?
I bet that the unlucky users who register for that email will see just more spam in their mailboxes in the future.
Again, ads per se are not unethical or "evil". It's the balance between content and ads that make it into something that may be perceived as unethical or "evil". When, after clicking a promising ad, I arrive at a page that contains virtually no information at all, just ads, then I'd say this classifies as unethical.
Dude, you are lucky. There are few real scams out there in Adsense country, but I have seen at least two real scams.
1) One service that promises a "life balance check" and only tells you in the fine print that by registering you agree to them sending you a 99 Euro bill for their "service". Scam!
2) A group of sites that disguises as real widget shops with nothing but ads ("sponsored links") above the fold. Once you enter a search term, the browser opens a new window AND goes into full screen mode. There is NO WAY OUT for the visitor except shooting down that window using the task manager (at first, users will click on the ads a few times, though, to get out). Scam!
But I agree that most of the junk sites are not scams but just arbitrage sites. Which is bad enough.