Don't worry it sucks as a user as well. Curiosity pushed me to use Google SSO to circumvent their crap one time, and they allowed themselves to subsequently spam my inbox with a flurry of emails. I proceeded to click the "unsubscribe" link in one of them, but to my surprise the spam kept coming. Turns out they have more than a dozen mailing settings and you have to painfully disable each one of them individually. Of course the simpler option is to mark all emails from pinterest.com as spam in the email client.

Especially as a site that specializes in hosting nearly exclusively non-original content, it's so ethically wrong for them to use such tactics.

Pinterest, Quora, Instagram, I never understood why people keep using these clearly unethical websites. Stop using them and other better alternatives will pop out, it's not like you depend on them like you depend on grocery shops or clothing stores. Voting with your attention is easy and cheap.