You can be almost certain that LinkedIn knew it was illegal when they did it, and accurately calculated that the fine they would receive (if any) would be much lower than the value derived from increased membership. In fact they would be stupid not to in winner-takes-all markets like social media.
Silicon Valley has a phrase for such flagrantly unethical practice, it is called "growth hacking".
Silicon Valley has a phrase for such flagrantly unethical practice, it is called "growth hacking".