You might as well say, "Let's do something evil, so that something good will come of it!" Some people even claim that we are saying this. But God is fair and will judge them as well.
Does this mean that the Law is sinful? Certainly not! But if it had not been for the Law, I would not have known what sin is really like. For example, I would not have known what it means to want something that belongs to someone else, unless the Law had told me not to do that.
Some godless people have sneaked in among us and are saying, "God treats us much better than we deserve, and so it is all right to be immoral." They even deny that we must obey Jesus Christ as our only Master and Lord. But long ago the Scriptures warned that these godless people were doomed.