Professionals should be paid for their performance even if it's based on bonuses. If someone goes above and beyond their normal duties, they should be compensated for their efforts and type. I do believe they should also have a base pay but incentives to work harder and earn more moeny.
In most professions, performance pay offers the best results in comparison to structured pay scales. A teacher that leads their students to higher test results is strengthening America's education system and deserves more than a teacher that produces lower results. Performance pay gives professionals an incentive to succeed and overperform in their duties, which is always desirable.