Innocence matters in the justice system. Your quote is fiction.
What Scalia actually said was:
This Court has never held that the Constitution forbids the execution of a convicted defendant who has had a full and fair trial but is later able to convince a habeas court that he is “actually” innocent.
In re Davis, 130 S. Ct. 1, 3 (2009).
This does not mean that "innocence doesn't matter." It means that if the defendant had a fair trial, and the defendant was convicted, and a state court of appeals affirmed the conviction, then the United States Constitution does not require a federal district court to additionally conduct a habeas review of the conviction, every time a defendant claims that he is innocent.
Should an actually innocent person be set free? Of course. Does that mean that the Constitution prescribes the writ of habeas corpus as the only way to get the job done? No. There are other mechanisms, such as parole, state-court habeas proceedings, pardons, and so on.
What can we, public, learn from this simple sentence long quoted/credited to the late US Justice?
We can learn that when our understanding of the facts is based on Internet memes, we're likely to be completely misinformed.
We can learn that we should review reliable sources before believing something unbelievable.
We can learn that it is possible that everything we believe is actually incorrect because we haven't been paying attention to whether we're being lied to.