Realistic vs. Idealistic

​​​In Question 96, Thomas Aquinas discusses the purpose and power of human law. He claims that the law isn't aimed for the benefit of the individual, but for that of the common good. This seems similar to the opinion of other philosophers such as Socrates and Aristotle. However, I found it interesting that Aquinas does not believe that human law has the ability, or even the right, to suppress all human vice. His philosophical predecessors banked heavily on human law to purge vice from our species; in Plato's Republic, Socrates debated which laws were necessary to create a city full of virtuous people. Aquinas, according to Article 2, appears to disagree with Plato and the others here; he says that "human law is framed for a number of human beings," all at varying levels of virtue, and that a vicious person should not be held to the same standard as a virtuous person. Here we see in Aquinas a level of realism not often appreciated by philosophers: he accepts that the law cannot condemn every immoral behavior. You can do something wrong without breaking the law - and Aquinas does not believe that this makes the law deficient. It's a very modern notion. For someone who is both a philosopher and a member of the Church, Aquinas might deserve respect purely on the grounds that he understands how human law plays out in practice. What do you think? Is Aquinas being realistic here, or is he maybe just being lazy, letting people wallow in their sin?