Scraping contact data in what way? Letting a user trigger some requests when they're moving between sites shouldn't be a problem at all.
But either way, that's not a reason to block links, and them being a competitor is not a reason to block links.
But either way, that's not a reason to block links, and them being a competitor is not a reason to block links.
Its naive that people sit on the sidelines opining they should've done the opposite when all the evidence points to blocking scraping as a standard business practice (and scraping is illegal if the company forbids it in their policy). Most people saying otherwise have not run a company or startup in a competitive environment where every other player wants to steal their lunch.
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.