I'd say the act of web scraping alone, is almost never unethical if you are careful to not cause undue load to servers. From an ethics, not legal perspective, I don't see a whole lot of difference between your computer's silicon eyes and your organic eyes just looking at something that's already in plain view.

It might be illegal in some jurisdiction; IANAL but I think you can just get out of that jurisdiction and scrape away if that is the case. It might violate some ToS but ToS isn't law; the consequences of violating a ToS are usually on the order of getting your IP banned.

What you do with the stuff you scraped can be ethical or unethical.

What makes it unethical?

Why should I be treated differently than search engine spiders?

If somebody doesn’t want their site scraped then they can let people know with robots.txt. Get off your high horse.

Likewise, just because its not legal or in some perspective its unethical, doesn't mean one should not do it.