With the limited context provided, this is the best I can give you (more information on the usefulness of reviews, their content and the identity of users would be helpful):
I consider these two different use cases.
Editing a "bad" opinion (I encourage you however to rethink the wording) with a change, an explanation, a new note, … is excellent for transparency. In case the user needs your contribution to realize his "mistake".
What happens if a user publishes something by accident? If they make a typo, do they do something wrong and post without realizing it? What happens when they realize that they have misunderstood something and want to delete the irrelevant and "bad" comments? They have to write? I find it uncomfortable for the user (bad for them) and also much less likely to happen (bad for you).
Regardless of this, I think users should be able to delete everything they create / publish. And in at least some cases, this is also legally required – have you checked?