If someone is crawling your content, that's usually bad behavior.
If a user signs up somewhere else, and wants their data to be ported over, there is very little to legitimately complain about. Even more so when the scraping is just contact data for that user, because that's very little server load.
Go away with this "steal their lunch" stuff. It should be legally mandated that users can transfer contacts between services.
Also blocking API access is very different from blocking user-posted links.