Both rhetoric and dialectic deal with persuasion and arranging arguments in a logical manner. However, they are different, as rhetoric is more focused on persuading the opponent or the audience no matter what is the truth. Dialectic, in its turn, is aimed at seeking the truth via logical assumptions. To my mind, dialectic is more noble than rhetoric, and I consider it a right practice.
Beyond any doubt, rhetoric can be useful in everyday life. It is very important for a person to prove something and to support any point of view. It can be a good tool for job interviews or for some intellectual debates organized for fun. However, it is a somewhat shallow and hypocritical practice, as it is not aimed at finding the real truth. If a person proves some point of view that they do not really believe, it is just a rhetorical exercise.
It can be argued that truth can be different, as depending on the beliefs, experience, and values each person has their own truth. However, although people should be able to see not only one point of view, they should understand that any truth is not absolute and that it is just a side of some multilateral issue. Dialectic helps to look from different points of view at the problem and to create a full vision of the situation. It unites the opposite points of view and leads to their synthesis. Thus, dialectics helps not to win the debate, but to, perhaps, change the point of view and to find some arguments that would become a common ground for a new dialogue with an opponent.
In conclusion, dialectic is a deeper practice compared to rhetoric. It allows to build a dialogue with an opponent at a new level and to become closer to the truth. It is more honest and flexible than a mere defending of some point of view that a person can even not share. Thus, it has the positive sides of rhetoric, as it is a good intellectual exercise, but it also has advantages that rhetoric lacks.