Not quite, actually. The elements of tortious interference vary by state but are roughly:
1) The existence of a contractual relationship or beneficial business relationship between two parties.
2) Knowledge of that relationship by a third party.
3) Intent of the third party to induce a party to the relationship to breach the relationship.
4) Lack of any privilege on the part of the third party to induce such a breach.
5) The contractual relationship is breached.
6) Damage to the party against whom the breach occurs.
Yelp may have a case for tortious interference against the restaurant if they are paying customers to break their Yelp terms. Yelp still sucks.
Your missing a major caveat. Completion is still encouraged so for example poaching employees is still generally legal. As long as you don't use "improper means or methods".
